diff --git a/conanfile.py b/conanfile.py
index ff27e6cc..d8d8e141 100644
--- a/conanfile.py
+++ b/conanfile.py
@@ -104,7 +104,7 @@ class MPUnitsConan(ConanFile):
     def requirements(self):
         self.requires("gsl-lite/0.40.0")
         if self._use_libfmt:
-            self.requires("fmt/10.1.0")
+            self.requires("fmt/10.1.1")
 
     def build_requirements(self):
         if self._build_all:
diff --git a/example/CMakeLists.txt b/example/CMakeLists.txt
index 5c4bc3c4..33d09727 100644
--- a/example/CMakeLists.txt
+++ b/example/CMakeLists.txt
@@ -22,15 +22,25 @@
 
 cmake_minimum_required(VERSION 3.5)
 
+# find dependencies
+if(NOT TARGET gsl::gsl-lite)
+    find_package(gsl-lite CONFIG REQUIRED)
+endif()
+
 add_library(example_utils INTERFACE)
 target_include_directories(example_utils INTERFACE include)
+target_link_libraries(example_utils INTERFACE gsl::gsl-lite)
 
 #
-# add_example(target <depependencies>...)
+# add_example(target <mp-units-depependencies>...)
 #
 function(add_example target)
     add_executable(${target} ${target}.cpp)
-    target_link_libraries(${target} PRIVATE ${ARGN})
+    if(TARGET mp-units::modules)
+        target_link_libraries(${target} PRIVATE mp-units::modules)
+    else()
+        target_link_libraries(${target} PRIVATE ${ARGN})
+    endif()
 endfunction()
 
 add_example(avg_speed mp-units::core-io mp-units::si mp-units::cgs mp-units::usc)
@@ -49,7 +59,8 @@ add_example(
 add_example(conversion_factor mp-units::core-fmt mp-units::core-io mp-units::si)
 add_example(currency mp-units::core-io)
 add_example(foot_pound_second mp-units::core-fmt mp-units::international mp-units::imperial)
-add_example(glide_computer mp-units::core-fmt mp-units::international mp-units::utility glide_computer_lib)
+add_example(glide_computer mp-units::core-fmt mp-units::international mp-units::utility)
+target_link_libraries(glide_computer PRIVATE glide_computer_lib)
 add_example(hello_units mp-units::core-fmt mp-units::core-io mp-units::si mp-units::usc)
 add_example(measurement mp-units::core-io mp-units::si)
 add_example(si_constants mp-units::core-fmt mp-units::si)
@@ -60,14 +71,9 @@ add_example(
 )
 add_example(total_energy mp-units::core-io mp-units::si mp-units::natural mp-units::utility)
 add_example(
-    unmanned_aerial_vehicle
-    mp-units::core-fmt
-    mp-units::core-io
-    mp-units::si
-    mp-units::international
-    mp-units::utility
-    example_utils
+    unmanned_aerial_vehicle mp-units::core-fmt mp-units::core-io mp-units::si mp-units::international mp-units::utility
 )
+target_link_libraries(unmanned_aerial_vehicle PRIVATE example_utils)
 
 add_subdirectory(glide_computer_lib)
 add_subdirectory(kalman_filter)
diff --git a/example/avg_speed.cpp b/example/avg_speed.cpp
index 6744ede1..4443fb6d 100644
--- a/example/avg_speed.cpp
+++ b/example/avg_speed.cpp
@@ -25,13 +25,17 @@
 // !!! renders correctly in the documentation "Examples" section.                 !!!
 // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
+#include <exception>
+#include <iostream>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/ostream.h>
 #include <mp-units/systems/cgs/cgs.h>
 #include <mp-units/systems/international/international.h>
-#include <mp-units/systems/isq/isq.h>
-#include <mp-units/systems/si/si.h>
-#include <exception>
-#include <iostream>
+#include <mp-units/systems/isq/space_and_time.h>
+#include <mp-units/systems/si/unit_symbols.h>
+#endif
 
 namespace {
 
diff --git a/example/capacitor_time_curve.cpp b/example/capacitor_time_curve.cpp
index d1fb12ce..02bbc271 100644
--- a/example/capacitor_time_curve.cpp
+++ b/example/capacitor_time_curve.cpp
@@ -20,11 +20,15 @@
     physical_quantities
 */
 
+#include <iostream>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/math.h>  // IWYU pragma: keep
 #include <mp-units/ostream.h>
 #include <mp-units/systems/isq/electromagnetism.h>
 #include <mp-units/systems/si/si.h>
-#include <iostream>
+#endif
 
 int main()
 {
diff --git a/example/clcpp_response.cpp b/example/clcpp_response.cpp
index fb9f93e3..58cdd912 100644
--- a/example/clcpp_response.cpp
+++ b/example/clcpp_response.cpp
@@ -15,6 +15,11 @@
  along with this program. If not, see http://www.gnu.org/licenses./
 */
 
+#include <mp-units/bits/fmt_hacks.h>
+#include <iostream>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/format.h>
 #include <mp-units/ostream.h>
 #include <mp-units/systems/iau/iau.h>
@@ -24,7 +29,7 @@
 #include <mp-units/systems/si/si.h>
 #include <mp-units/systems/typographic/typographic.h>
 #include <mp-units/systems/usc/usc.h>
-#include <iostream>
+#endif
 
 namespace {
 
diff --git a/example/conversion_factor.cpp b/example/conversion_factor.cpp
index 5a4eaa97..2b666b9c 100644
--- a/example/conversion_factor.cpp
+++ b/example/conversion_factor.cpp
@@ -15,12 +15,17 @@
  along with this program. If not, see http://www.gnu.org/licenses./
 */
 
+#include <mp-units/bits/fmt_hacks.h>
+#include <iostream>
+#include <type_traits>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/format.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/unit_symbols.h>
 #include <mp-units/systems/si/units.h>
-#include <iostream>
-#include <type_traits>
+#endif
 
 /*
   get conversion factor from one dimensionally equivalent
diff --git a/example/currency.cpp b/example/currency.cpp
index 28af832e..57cf5a57 100644
--- a/example/currency.cpp
+++ b/example/currency.cpp
@@ -20,11 +20,16 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#include <mp-units/quantity_spec_macro.h>
+#include <iostream>
+#include <map>
+#ifdef MP_UNITS_MODULES
+import mp_units.core_io;
+#else
 #include <mp-units/ostream.h>
 #include <mp-units/quantity.h>
 #include <mp-units/quantity_point.h>
-#include <iostream>
-#include <map>
+#endif
 
 using namespace mp_units;
 
diff --git a/example/foot_pound_second.cpp b/example/foot_pound_second.cpp
index 9177cd0c..bfb5719d 100644
--- a/example/foot_pound_second.cpp
+++ b/example/foot_pound_second.cpp
@@ -20,14 +20,19 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#include <mp-units/bits/fmt_hacks.h>
+#include <iostream>
+#include <string_view>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/format.h>
 #include <mp-units/systems/imperial/imperial.h>
 #include <mp-units/systems/international/international.h>
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/unit_symbols.h>
-#include <iostream>
-#include <string_view>
+#endif
 
 using namespace mp_units;
 using namespace mp_units::international::unit_symbols;
diff --git a/example/glide_computer.cpp b/example/glide_computer.cpp
index 09531727..cefe692e 100644
--- a/example/glide_computer.cpp
+++ b/example/glide_computer.cpp
@@ -22,10 +22,6 @@
 
 #include "glide_computer_lib.h"
 #include <mp-units/bits/fmt_hacks.h>
-#include <mp-units/chrono.h>
-#include <mp-units/math.h>
-#include <mp-units/systems/international/international.h>
-#include <mp-units/systems/si/unit_symbols.h>
 #include <array>
 #include <exception>
 #include <iostream>
@@ -33,6 +29,14 @@
 #include <string>
 #include <utility>
 #include <vector>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
+#include <mp-units/chrono.h>
+#include <mp-units/math.h>
+#include <mp-units/systems/international/international.h>
+#include <mp-units/systems/si/unit_symbols.h>
+#endif
 
 namespace {
 
diff --git a/example/glide_computer_lib/CMakeLists.txt b/example/glide_computer_lib/CMakeLists.txt
index 9534977d..65d11b35 100644
--- a/example/glide_computer_lib/CMakeLists.txt
+++ b/example/glide_computer_lib/CMakeLists.txt
@@ -23,5 +23,10 @@
 cmake_minimum_required(VERSION 3.5)
 
 add_library(glide_computer_lib STATIC glide_computer_lib.cpp include/glide_computer_lib.h)
-target_link_libraries(glide_computer_lib PRIVATE mp-units::core-fmt PUBLIC mp-units::si mp-units::utility example_utils)
+if(TARGET mp-units::modules)
+    target_link_libraries(glide_computer_lib PUBLIC gsl::gsl-lite mp-units::modules)
+else()
+    target_link_libraries(glide_computer_lib PRIVATE mp-units::core-fmt PUBLIC mp-units::si mp-units::utility)
+endif()
+target_link_libraries(glide_computer_lib PUBLIC example_utils)
 target_include_directories(glide_computer_lib PUBLIC include)
diff --git a/example/glide_computer_lib/glide_computer_lib.cpp b/example/glide_computer_lib/glide_computer_lib.cpp
index c0fa44d7..70d26edf 100644
--- a/example/glide_computer_lib/glide_computer_lib.cpp
+++ b/example/glide_computer_lib/glide_computer_lib.cpp
@@ -21,10 +21,14 @@
 // SOFTWARE.
 
 #include "glide_computer_lib.h"
-#include <mp-units/format.h>
 #include <iostream>
 #include <numeric>
 #include <string_view>
+#ifdef MP_UNITS_MODULES
+import mp_units.core_fmt;
+#else
+#include <mp-units/format.h>
+#endif
 
 namespace glide_computer {
 
diff --git a/example/glide_computer_lib/include/glide_computer_lib.h b/example/glide_computer_lib/include/glide_computer_lib.h
index daa3fcf5..50229a9b 100644
--- a/example/glide_computer_lib/include/glide_computer_lib.h
+++ b/example/glide_computer_lib/include/glide_computer_lib.h
@@ -22,11 +22,9 @@
 
 #pragma once
 
+#include <mp-units/quantity_spec_macro.h>
+//
 #include "geographic.h"
-#include <mp-units/chrono.h>
-#include <mp-units/math.h>  // IWYU pragma: keep
-#include <mp-units/quantity_point.h>
-#include <mp-units/systems/isq/space_and_time.h>
 #include <algorithm>
 #include <array>
 #include <initializer_list>
@@ -35,6 +33,14 @@
 #include <ranges>
 #include <string>  // IWYU pragma: keep
 #include <vector>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
+#include <mp-units/chrono.h>
+#include <mp-units/math.h>  // IWYU pragma: keep
+#include <mp-units/quantity_point.h>
+#include <mp-units/systems/isq/space_and_time.h>
+#endif
 
 // An example of a really simplified tactical glide computer
 // Simplifications:
diff --git a/example/hello_units.cpp b/example/hello_units.cpp
index e537a7a6..6bc12235 100644
--- a/example/hello_units.cpp
+++ b/example/hello_units.cpp
@@ -25,12 +25,17 @@
 // !!! renders correctly in the documentation "Examples" section.                 !!!
 // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
+#include <mp-units/bits/fmt_hacks.h>
+#include <iostream>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/format.h>
 #include <mp-units/ostream.h>
 #include <mp-units/systems/international/international.h>
 #include <mp-units/systems/isq/isq.h>
 #include <mp-units/systems/si/si.h>
-#include <iostream>
+#endif
 
 using namespace mp_units;
 
diff --git a/example/include/geographic.h b/example/include/geographic.h
index f66fd1cf..ade0f6e0 100644
--- a/example/include/geographic.h
+++ b/example/include/geographic.h
@@ -24,6 +24,13 @@
 
 #include "ranged_representation.h"
 #include <mp-units/bits/fmt_hacks.h>
+#include <compare>
+#include <limits>
+#include <numbers>
+#include <ostream>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/compare.h>
 #include <mp-units/format.h>
 #include <mp-units/math.h>
@@ -31,10 +38,7 @@
 #include <mp-units/quantity_point.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/units.h>
-#include <compare>
-#include <limits>
-#include <numbers>
-#include <ostream>
+#endif
 
 namespace geographic {
 
diff --git a/example/include/ranged_representation.h b/example/include/ranged_representation.h
index 82f51846..2b7fff52 100644
--- a/example/include/ranged_representation.h
+++ b/example/include/ranged_representation.h
@@ -24,11 +24,15 @@
 
 #include "validated_type.h"
 #include <mp-units/bits/external/hacks.h>
-#include <mp-units/bits/fmt.h>
-#include <mp-units/customization_points.h>
 #include <algorithm>
 #include <concepts>
 #include <type_traits>
+#ifdef MP_UNITS_MODULES
+import mp_units.core;
+#else
+#include <mp-units/bits/fmt.h>
+#include <mp-units/customization_points.h>
+#endif
 
 template<std::movable T, MP_UNITS_CONSTRAINED_NTTP_WORKAROUND(std::convertible_to<T>) auto Min,
          MP_UNITS_CONSTRAINED_NTTP_WORKAROUND(std::convertible_to<T>) auto Max>
diff --git a/example/include/validated_type.h b/example/include/validated_type.h
index 15d540bc..77422ccc 100644
--- a/example/include/validated_type.h
+++ b/example/include/validated_type.h
@@ -23,11 +23,16 @@
 #pragma once
 
 #include <gsl/gsl-lite.hpp>
+#include <mp-units/bits/fmt_hacks.h>
+#include <ostream>
+#include <utility>
+#ifdef MP_UNITS_MODULES
+import mp_units.core_fmt;
+#else
 #include <mp-units/bits/external/hacks.h>
 #include <mp-units/bits/fmt.h>
 #include <mp-units/customization_points.h>
-#include <ostream>
-#include <utility>
+#endif
 
 inline constexpr struct validated_tag {
 } validated;
diff --git a/example/kalman_filter/CMakeLists.txt b/example/kalman_filter/CMakeLists.txt
index ef91cdcb..4c7954d9 100644
--- a/example/kalman_filter/CMakeLists.txt
+++ b/example/kalman_filter/CMakeLists.txt
@@ -27,7 +27,11 @@ cmake_minimum_required(VERSION 3.5)
 #
 function(add_example target)
     add_executable(${target} ${target}.cpp)
-    target_link_libraries(${target} PRIVATE ${ARGN})
+    if(TARGET mp-units::modules)
+        target_link_libraries(${target} PRIVATE mp-units::modules)
+    else()
+        target_link_libraries(${target} PRIVATE ${ARGN})
+    endif()
 endfunction()
 
 add_example(kalman_filter-example_1 mp-units::core-fmt mp-units::si mp-units::utility)
diff --git a/example/kalman_filter/kalman.h b/example/kalman_filter/kalman.h
index dd925f55..310d9941 100644
--- a/example/kalman_filter/kalman.h
+++ b/example/kalman_filter/kalman.h
@@ -23,12 +23,16 @@
 #pragma once
 
 #include <mp-units/bits/fmt_hacks.h>
+#include <tuple>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/format.h>
 #include <mp-units/math.h>
 #include <mp-units/quantity.h>
 #include <mp-units/quantity_point.h>
 #include <mp-units/systems/isq/space_and_time.h>
-#include <tuple>
+#endif
 
 namespace kalman {
 
diff --git a/example/kalman_filter/kalman_filter-example_1.cpp b/example/kalman_filter/kalman_filter-example_1.cpp
index bee71761..c038f253 100644
--- a/example/kalman_filter/kalman_filter-example_1.cpp
+++ b/example/kalman_filter/kalman_filter-example_1.cpp
@@ -21,11 +21,15 @@
 // SOFTWARE.
 
 #include "kalman.h"
+#include <array>
+#include <iostream>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/format.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/unit_symbols.h>
-#include <array>
-#include <iostream>
+#endif
 
 // Based on: https://www.kalmanfilter.net/alphabeta.html#ex1
 
diff --git a/example/kalman_filter/kalman_filter-example_2.cpp b/example/kalman_filter/kalman_filter-example_2.cpp
index ac748ca3..0260d2de 100644
--- a/example/kalman_filter/kalman_filter-example_2.cpp
+++ b/example/kalman_filter/kalman_filter-example_2.cpp
@@ -21,11 +21,15 @@
 // SOFTWARE.
 
 #include "kalman.h"
+#include <array>
+#include <iostream>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/format.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/unit_symbols.h>
-#include <array>
-#include <iostream>
+#endif
 
 // Based on: https://www.kalmanfilter.net/alphabeta.html#ex2
 
diff --git a/example/kalman_filter/kalman_filter-example_3.cpp b/example/kalman_filter/kalman_filter-example_3.cpp
index 1fb2e32f..5d453d48 100644
--- a/example/kalman_filter/kalman_filter-example_3.cpp
+++ b/example/kalman_filter/kalman_filter-example_3.cpp
@@ -21,11 +21,15 @@
 // SOFTWARE.
 
 #include "kalman.h"
+#include <array>
+#include <iostream>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/format.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/unit_symbols.h>
-#include <array>
-#include <iostream>
+#endif
 
 // Based on: https://www.kalmanfilter.net/alphabeta.html#ex3
 
diff --git a/example/kalman_filter/kalman_filter-example_4.cpp b/example/kalman_filter/kalman_filter-example_4.cpp
index cc5044ea..00696c02 100644
--- a/example/kalman_filter/kalman_filter-example_4.cpp
+++ b/example/kalman_filter/kalman_filter-example_4.cpp
@@ -21,11 +21,15 @@
 // SOFTWARE.
 
 #include "kalman.h"
+#include <array>
+#include <iostream>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/format.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/unit_symbols.h>
-#include <array>
-#include <iostream>
+#endif
 
 // Based on: https://www.kalmanfilter.net/alphabeta.html#ex4
 
diff --git a/example/kalman_filter/kalman_filter-example_5.cpp b/example/kalman_filter/kalman_filter-example_5.cpp
index e50114eb..b4be7e3c 100644
--- a/example/kalman_filter/kalman_filter-example_5.cpp
+++ b/example/kalman_filter/kalman_filter-example_5.cpp
@@ -21,12 +21,16 @@
 // SOFTWARE.
 
 #include "kalman.h"
+#include <array>
+#include <iostream>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/format.h>
 #include <mp-units/math.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/unit_symbols.h>
-#include <array>
-#include <iostream>
+#endif
 
 // Based on: https://www.kalmanfilter.net/kalman1d.html#ex5
 
diff --git a/example/kalman_filter/kalman_filter-example_6.cpp b/example/kalman_filter/kalman_filter-example_6.cpp
index 23660370..a6ab2131 100644
--- a/example/kalman_filter/kalman_filter-example_6.cpp
+++ b/example/kalman_filter/kalman_filter-example_6.cpp
@@ -21,13 +21,17 @@
 // SOFTWARE.
 
 #include "kalman.h"
+#include <array>
+#include <iostream>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/format.h>
 #include <mp-units/math.h>
 #include <mp-units/quantity_point.h>
 #include <mp-units/systems/isq/thermodynamics.h>
 #include <mp-units/systems/si/si.h>
-#include <array>
-#include <iostream>
+#endif
 
 // Based on: https://www.kalmanfilter.net/kalman1d.html#ex6
 
diff --git a/example/kalman_filter/kalman_filter-example_7.cpp b/example/kalman_filter/kalman_filter-example_7.cpp
index d82d7323..49c832fe 100644
--- a/example/kalman_filter/kalman_filter-example_7.cpp
+++ b/example/kalman_filter/kalman_filter-example_7.cpp
@@ -21,13 +21,17 @@
 // SOFTWARE.
 
 #include "kalman.h"
+#include <array>
+#include <iostream>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/format.h>
 #include <mp-units/math.h>
 #include <mp-units/quantity_point.h>
 #include <mp-units/systems/isq/thermodynamics.h>
 #include <mp-units/systems/si/si.h>
-#include <array>
-#include <iostream>
+#endif
 
 // Based on: https://www.kalmanfilter.net/kalman1d.html#ex7
 
diff --git a/example/kalman_filter/kalman_filter-example_8.cpp b/example/kalman_filter/kalman_filter-example_8.cpp
index ca02b7bd..474ecff7 100644
--- a/example/kalman_filter/kalman_filter-example_8.cpp
+++ b/example/kalman_filter/kalman_filter-example_8.cpp
@@ -21,13 +21,17 @@
 // SOFTWARE.
 
 #include "kalman.h"
+#include <array>
+#include <iostream>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/format.h>
 #include <mp-units/math.h>
 #include <mp-units/quantity_point.h>
 #include <mp-units/systems/isq/thermodynamics.h>
 #include <mp-units/systems/si/si.h>
-#include <array>
-#include <iostream>
+#endif
 
 // Based on: https://www.kalmanfilter.net/kalman1d.html#ex8
 
diff --git a/example/measurement.cpp b/example/measurement.cpp
index cd36aa92..0f3813e7 100644
--- a/example/measurement.cpp
+++ b/example/measurement.cpp
@@ -20,13 +20,17 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#include <cmath>
+#include <exception>
+#include <iostream>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/ostream.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/unit_symbols.h>
 #include <mp-units/systems/si/units.h>
-#include <cmath>
-#include <exception>
-#include <iostream>
+#endif
 
 namespace {
 
diff --git a/example/si_constants.cpp b/example/si_constants.cpp
index 255f8054..35d855d5 100644
--- a/example/si_constants.cpp
+++ b/example/si_constants.cpp
@@ -25,9 +25,14 @@
 // !!! renders correctly in the documentation "Examples" section.                 !!!
 // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
+#include <mp-units/bits/fmt_hacks.h>
+#include <iostream>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/format.h>
 #include <mp-units/systems/si/si.h>
-#include <iostream>
+#endif
 
 template<class T>
   requires mp_units::is_scalar<T>
diff --git a/example/spectroscopy_units.cpp b/example/spectroscopy_units.cpp
index 363605a1..7a6270d6 100644
--- a/example/spectroscopy_units.cpp
+++ b/example/spectroscopy_units.cpp
@@ -20,11 +20,16 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#include <mp-units/bits/fmt_hacks.h>
+#include <iostream>
+#include <tuple>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/format.h>
 #include <mp-units/systems/isq/isq.h>
 #include <mp-units/systems/si/si.h>
-#include <iostream>
-#include <tuple>
+#endif
 
 // This example implements a table of units provided in the following article
 // http://cds.cern.ch/record/1481609/files/978-3-642-18018-7_BookBackMatter.pdf
diff --git a/example/storage_tank.cpp b/example/storage_tank.cpp
index d975e9e0..84d1c42c 100644
--- a/example/storage_tank.cpp
+++ b/example/storage_tank.cpp
@@ -20,6 +20,16 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#include <mp-units/bits/fmt_hacks.h>
+#include <mp-units/quantity_spec_macro.h>
+#include <cassert>
+#include <chrono>
+#include <iostream>
+#include <numbers>
+#include <utility>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/chrono.h>
 #include <mp-units/format.h>
 #include <mp-units/math.h>
@@ -28,11 +38,7 @@
 #include <mp-units/systems/si/constants.h>
 #include <mp-units/systems/si/unit_symbols.h>
 #include <mp-units/systems/si/units.h>
-#include <cassert>
-#include <chrono>
-#include <iostream>
-#include <numbers>
-#include <utility>
+#endif
 
 // allows standard gravity (acceleration) and weight (force) to be expressed with scalar representation
 // types instead of requiring the usage of Linear Algebra library for this simple example
diff --git a/example/strong_angular_quantities.cpp b/example/strong_angular_quantities.cpp
index 7d375e3c..298a097e 100644
--- a/example/strong_angular_quantities.cpp
+++ b/example/strong_angular_quantities.cpp
@@ -20,11 +20,15 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#include <iostream>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/math.h>
 #include <mp-units/ostream.h>
 #include <mp-units/systems/isq_angle/isq_angle.h>
 #include <mp-units/systems/si/unit_symbols.h>
-#include <iostream>
+#endif
 
 template<class T>
   requires mp_units::is_scalar<T>
diff --git a/example/total_energy.cpp b/example/total_energy.cpp
index fa83a6cd..116ac4ad 100644
--- a/example/total_energy.cpp
+++ b/example/total_energy.cpp
@@ -20,14 +20,18 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#include <exception>
+#include <iostream>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/math.h>
 #include <mp-units/ostream.h>
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/natural/natural.h>
 #include <mp-units/systems/si/constants.h>
 #include <mp-units/systems/si/unit_symbols.h>
-#include <exception>
-#include <iostream>
+#endif
 
 template<class T>
   requires mp_units::is_scalar<T>
@@ -56,31 +60,21 @@ void si_example()
 
   std::cout << "\n*** SI units (c = " << c << " = " << c.in(si::metre / s) << ") ***\n";
 
-  std::cout << "\n[in `GeV` and `c`]\n"
-            << "p = " << p1 << "\n"
-            << "m = " << m1 << "\n"
-            << "E = " << E << "\n";
+  std::cout << "\n[in `GeV` and `c`]\n" << "p = " << p1 << "\n" << "m = " << m1 << "\n" << "E = " << E << "\n";
 
   const auto p2 = p1.in(GeV / (m / s));
   const auto m2 = m1.in(GeV / pow<2>(m / s));
   const auto E2 = total_energy(p2, m2, c).in(GeV);
 
-  std::cout << "\n[in `GeV`]\n"
-            << "p = " << p2 << "\n"
-            << "m = " << m2 << "\n"
-            << "E = " << E2 << "\n";
+  std::cout << "\n[in `GeV`]\n" << "p = " << p2 << "\n" << "m = " << m2 << "\n" << "E = " << E2 << "\n";
 
   const auto p3 = p1.in(kg * m / s);
   const auto m3 = m1.in(kg);
   const auto E3 = total_energy(p3, m3, c).in(J);
 
-  std::cout << "\n[in SI base units]\n"
-            << "p = " << p3 << "\n"
-            << "m = " << m3 << "\n"
-            << "E = " << E3 << "\n";
+  std::cout << "\n[in SI base units]\n" << "p = " << p3 << "\n" << "m = " << m3 << "\n" << "E = " << E3 << "\n";
 
-  std::cout << "\n[converted from SI units back to GeV]\n"
-            << "E = " << E3.force_in(GeV) << "\n";
+  std::cout << "\n[converted from SI units back to GeV]\n" << "E = " << E3.force_in(GeV) << "\n";
 }
 
 void natural_example()
diff --git a/example/unmanned_aerial_vehicle.cpp b/example/unmanned_aerial_vehicle.cpp
index fe465f68..6e089939 100644
--- a/example/unmanned_aerial_vehicle.cpp
+++ b/example/unmanned_aerial_vehicle.cpp
@@ -21,13 +21,18 @@
 // SOFTWARE.
 
 #include "geographic.h"
+#include <mp-units/bits/fmt_hacks.h>
+#include <cassert>
+#include <iostream>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/ostream.h>
 #include <mp-units/quantity_point.h>
 #include <mp-units/systems/international/international.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/unit_symbols.h>
-#include <cassert>
-#include <iostream>
+#endif
 
 using namespace mp_units;
 using namespace geographic;
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 739e553e..0c5a3fe7 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -28,6 +28,9 @@ set(projectPrefix MP_UNITS_)
 option(${projectPrefix}AS_SYSTEM_HEADERS "Exports library as system headers" OFF)
 message(STATUS "${projectPrefix}AS_SYSTEM_HEADERS: ${${projectPrefix}AS_SYSTEM_HEADERS}")
 
+option(${projectPrefix}BUILD_CXX_MODULES "Add C++ modules to the list of default targets" OFF)
+message(STATUS "${projectPrefix}BUILD_CXX_MODULES: ${${projectPrefix}BUILD_CXX_MODULES}")
+
 list(APPEND CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/cmake")
 
 include(AddUnitsModule)
@@ -37,7 +40,9 @@ if(${projectPrefix}AS_SYSTEM_HEADERS)
     set(unitsAsSystem SYSTEM)
 endif()
 
+add_subdirectory(core-macros)
 add_subdirectory(core)
+add_subdirectory(core-fmt-macros)
 add_subdirectory(core-fmt)
 add_subdirectory(core-io)
 add_subdirectory(systems)
@@ -51,6 +56,59 @@ target_link_libraries(
 add_library(mp-units::mp-units ALIAS mp-units)
 install(TARGETS mp-units EXPORT mp-unitsTargets)
 
+# C++ modules
+if(${projectPrefix}BUILD_CXX_MODULES)
+    add_library(mp-units-core-module)
+    add_library(mp-units::core-module ALIAS mp-units-core-module)
+    target_sources(
+        mp-units-core-module PUBLIC FILE_SET CXX_MODULES BASE_DIRS "${CMAKE_CURRENT_SOURCE_DIR}" FILES
+                                    "mp-units-core.cpp"
+    )
+    target_compile_definitions(mp-units-core-module INTERFACE MP_UNITS_MODULES)
+    target_link_libraries(mp-units-core-module PRIVATE mp-units::core PUBLIC mp-units::core-macros)
+    if(CMAKE_CXX_COMPILER_ID MATCHES ".*Clang" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 18)
+        target_compile_options(mp-units-core-module PUBLIC "-Wno-include-angled-in-module-purview")
+    endif()
+
+    add_library(mp-units-core-fmt-module)
+    add_library(mp-units::core-fmt-module ALIAS mp-units-core-fmt-module)
+    target_sources(
+        mp-units-core-fmt-module PUBLIC FILE_SET CXX_MODULES BASE_DIRS "${CMAKE_CURRENT_SOURCE_DIR}" FILES
+                                        "mp-units-core-fmt.cpp"
+    )
+    target_link_libraries(
+        mp-units-core-fmt-module PRIVATE mp-units::core-fmt PUBLIC mp-units::core-fmt-macros mp-units::core-module
+    )
+
+    add_library(mp-units-core-io-module)
+    add_library(mp-units::core-io-module ALIAS mp-units-core-io-module)
+    target_sources(
+        mp-units-core-io-module PUBLIC FILE_SET CXX_MODULES BASE_DIRS "${CMAKE_CURRENT_SOURCE_DIR}" FILES
+                                       "mp-units-core-io.cpp"
+    )
+    target_link_libraries(mp-units-core-io-module PRIVATE mp-units::core-io PUBLIC mp-units::core-module)
+
+    add_library(mp-units-systems-module)
+    add_library(mp-units::systems-module ALIAS mp-units-systems-module)
+    target_sources(
+        mp-units-systems-module PUBLIC FILE_SET CXX_MODULES BASE_DIRS "${CMAKE_CURRENT_SOURCE_DIR}" FILES
+                                       "mp-units-systems.cpp"
+    )
+    target_link_libraries(
+        mp-units-systems-module PRIVATE mp-units::systems mp-units::utility PUBLIC mp-units::core-module
+    )
+
+    add_library(mp-units-modules)
+    add_library(mp-units::modules ALIAS mp-units-modules)
+    target_sources(
+        mp-units-modules PUBLIC FILE_SET CXX_MODULES BASE_DIRS "${CMAKE_CURRENT_SOURCE_DIR}" FILES "mp-units.cpp"
+    )
+    target_link_libraries(
+        mp-units-modules PUBLIC mp-units::core-module mp-units::core-fmt-module mp-units::core-io-module
+                                mp-units::systems-module
+    )
+endif()
+
 # local build
 export(EXPORT mp-unitsTargets NAMESPACE mp-units::)
 configure_file("mp-unitsConfig.cmake" "." COPYONLY)
diff --git a/src/core-fmt-macros/CMakeLists.txt b/src/core-fmt-macros/CMakeLists.txt
new file mode 100644
index 00000000..8f6bc13c
--- /dev/null
+++ b/src/core-fmt-macros/CMakeLists.txt
@@ -0,0 +1,45 @@
+# The MIT License (MIT)
+#
+# Copyright (c) 2018 Mateusz Pusz
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+cmake_minimum_required(VERSION 3.19)
+
+# core-fmt-macros library definition
+add_library(mp-units-core-fmt-macros INTERFACE include/mp-units/bits/fmt_hacks.h)
+target_include_directories(
+    mp-units-core-fmt-macros ${unitsAsSystem} INTERFACE $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+                                                        $<INSTALL_INTERFACE:include>
+)
+target_link_libraries(mp-units-core-fmt-macros INTERFACE mp-units::core-macros)
+
+if(${projectPrefix}USE_LIBFMT)
+    if(NOT TARGET fmt::fmt)
+        find_package(fmt CONFIG REQUIRED)
+    endif()
+    target_link_libraries(mp-units-core-fmt-macros INTERFACE fmt::fmt)
+endif()
+
+set_target_properties(mp-units-core-fmt-macros PROPERTIES EXPORT_NAME core-fmt-macros)
+add_library(mp-units::core-fmt-macros ALIAS mp-units-core-fmt-macros)
+
+# installation
+install(TARGETS mp-units-core-fmt-macros EXPORT mp-unitsTargets)
+install(DIRECTORY include/mp-units TYPE INCLUDE)
diff --git a/src/core-fmt/include/mp-units/bits/fmt_hacks.h b/src/core-fmt-macros/include/mp-units/bits/fmt_hacks.h
similarity index 99%
rename from src/core-fmt/include/mp-units/bits/fmt_hacks.h
rename to src/core-fmt-macros/include/mp-units/bits/fmt_hacks.h
index 008c3159..3ac40aad 100644
--- a/src/core-fmt/include/mp-units/bits/fmt_hacks.h
+++ b/src/core-fmt-macros/include/mp-units/bits/fmt_hacks.h
@@ -27,6 +27,8 @@
 //
 // For the license information refer to format.h.
 
+#pragma once
+
 #include <mp-units/bits/external/hacks.h>
 
 #ifndef MP_UNITS_USE_LIBFMT
diff --git a/src/core-fmt/CMakeLists.txt b/src/core-fmt/CMakeLists.txt
index 99f2ce04..35a59370 100644
--- a/src/core-fmt/CMakeLists.txt
+++ b/src/core-fmt/CMakeLists.txt
@@ -27,6 +27,7 @@ message(STATUS "${projectPrefix}USE_LIBFMT: ${${projectPrefix}USE_LIBFMT}")
 
 add_units_module(core-fmt DEPENDENCIES mp-units::core HEADERS include/mp-units/format.h)
 target_compile_definitions(mp-units-core-fmt INTERFACE ${projectPrefix}USE_LIBFMT=$<BOOL:${${projectPrefix}USE_LIBFMT}>)
+target_link_libraries(mp-units-core-fmt INTERFACE mp-units::core-fmt-macros)
 
 if(${projectPrefix}USE_LIBFMT)
     if(NOT TARGET fmt::fmt)
diff --git a/src/core-macros/CMakeLists.txt b/src/core-macros/CMakeLists.txt
new file mode 100644
index 00000000..38bfe974
--- /dev/null
+++ b/src/core-macros/CMakeLists.txt
@@ -0,0 +1,40 @@
+# The MIT License (MIT)
+#
+# Copyright (c) 2018 Mateusz Pusz
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+cmake_minimum_required(VERSION 3.19)
+
+# core-macros library definition
+add_library(
+    mp-units-core-macros INTERFACE include/mp-units/bits/external/hacks.h include/mp-units/quantity_spec_macro.h
+)
+target_compile_features(mp-units-core-macros INTERFACE cxx_std_20)
+target_include_directories(
+    mp-units-core-macros ${unitsAsSystem} INTERFACE $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+                                                    $<INSTALL_INTERFACE:include>
+)
+
+set_target_properties(mp-units-core-macros PROPERTIES EXPORT_NAME core-macros)
+add_library(mp-units::core-macros ALIAS mp-units-core-macros)
+
+# installation
+install(TARGETS mp-units-core-macros EXPORT mp-unitsTargets)
+install(DIRECTORY include/mp-units TYPE INCLUDE)
diff --git a/src/core-macros/include/mp-units/bits/core-gmf.h b/src/core-macros/include/mp-units/bits/core-gmf.h
new file mode 100644
index 00000000..fdcd10ad
--- /dev/null
+++ b/src/core-macros/include/mp-units/bits/core-gmf.h
@@ -0,0 +1,50 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2018 Mateusz Pusz
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#pragma once
+
+// core
+#include <gsl/gsl-lite.hpp>
+#include <mp-units/bits/external/hacks.h>
+#include <array>
+#include <compare>
+#include <concepts>
+#include <cstddef>
+#include <cstdint>
+#include <functional>
+#include <initializer_list>
+#include <iterator>
+#include <limits>
+#include <numbers>
+#include <numeric>
+#include <optional>
+#include <ranges>
+#include <string>
+#include <string_view>
+#include <tuple>
+#include <type_traits>
+#include <utility>
+
+// utility
+#include <chrono>
+#include <cmath>
+#include <random>
diff --git a/src/core/include/mp-units/bits/external/hacks.h b/src/core-macros/include/mp-units/bits/external/hacks.h
similarity index 100%
rename from src/core/include/mp-units/bits/external/hacks.h
rename to src/core-macros/include/mp-units/bits/external/hacks.h
diff --git a/src/core-macros/include/mp-units/quantity_spec_macro.h b/src/core-macros/include/mp-units/quantity_spec_macro.h
new file mode 100644
index 00000000..9e45b833
--- /dev/null
+++ b/src/core-macros/include/mp-units/quantity_spec_macro.h
@@ -0,0 +1,37 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2018 Mateusz Pusz
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#pragma once
+
+#ifdef __cpp_explicit_this_parameter
+
+#define QUANTITY_SPEC(name, ...)                                          \
+  inline constexpr struct name : ::mp_units::quantity_spec<__VA_ARGS__> { \
+  } name
+
+#else
+
+#define QUANTITY_SPEC(name, ...)                                                \
+  inline constexpr struct name : ::mp_units::quantity_spec<name, __VA_ARGS__> { \
+  } name
+
+#endif
diff --git a/src/core/CMakeLists.txt b/src/core/CMakeLists.txt
index 7159996e..0abde4e6 100644
--- a/src/core/CMakeLists.txt
+++ b/src/core/CMakeLists.txt
@@ -33,7 +33,6 @@ add_library(
     INTERFACE
     include/mp-units/bits/external/algorithm.h
     include/mp-units/bits/external/fixed_string.h
-    include/mp-units/bits/external/hacks.h
     include/mp-units/bits/external/math_concepts.h
     include/mp-units/bits/external/prime.h
     include/mp-units/bits/external/type_list.h
@@ -44,6 +43,7 @@ add_library(
     include/mp-units/bits/get_associated_quantity.h
     include/mp-units/bits/get_common_base.h
     include/mp-units/bits/magnitude.h
+    include/mp-units/bits/math_core.h
     include/mp-units/bits/quantity_cast.h
     include/mp-units/bits/quantity_concepts.h
     include/mp-units/bits/quantity_point_concepts.h
@@ -67,8 +67,7 @@ add_library(
     include/mp-units/system_reference.h
     include/mp-units/unit.h
 )
-target_compile_features(mp-units-core INTERFACE cxx_std_20)
-target_link_libraries(mp-units-core INTERFACE gsl::gsl-lite)
+target_link_libraries(mp-units-core INTERFACE gsl::gsl-lite mp-units::core-macros)
 target_include_directories(
     mp-units-core ${unitsAsSystem} INTERFACE $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
                                              $<INSTALL_INTERFACE:include>
diff --git a/src/utility/include/mp-units/bits/math_core.h b/src/core/include/mp-units/bits/math_core.h
similarity index 100%
rename from src/utility/include/mp-units/bits/math_core.h
rename to src/core/include/mp-units/bits/math_core.h
diff --git a/src/core/include/mp-units/core.h b/src/core/include/mp-units/core.h
index b6c3682d..209076f0 100644
--- a/src/core/include/mp-units/core.h
+++ b/src/core/include/mp-units/core.h
@@ -22,6 +22,7 @@
 
 #pragma once
 
+#include <mp-units/bits/math_core.h>
 #include <mp-units/concepts.h>
 #include <mp-units/customization_points.h>
 #include <mp-units/dimension.h>
diff --git a/src/core/include/mp-units/quantity_spec.h b/src/core/include/mp-units/quantity_spec.h
index c9b242d4..4550c1e7 100644
--- a/src/core/include/mp-units/quantity_spec.h
+++ b/src/core/include/mp-units/quantity_spec.h
@@ -32,6 +32,7 @@
 #include <mp-units/bits/reference_concepts.h>
 #include <mp-units/bits/representation_concepts.h>
 #include <mp-units/dimension.h>
+#include <mp-units/quantity_spec_macro.h>
 #include <tuple>
 
 namespace mp_units {
@@ -364,20 +365,6 @@ struct quantity_spec<Self, QS, Eq, Args...> : quantity_spec<Self, QS, Args...> {
   static constexpr quantity_character character = detail::quantity_character_init<Args...>(Eq.character);
 };
 
-#ifdef __cpp_explicit_this_parameter
-
-#define QUANTITY_SPEC(name, ...)                                          \
-  inline constexpr struct name : ::mp_units::quantity_spec<__VA_ARGS__> { \
-  } name
-
-#else
-
-#define QUANTITY_SPEC(name, ...)                                                \
-  inline constexpr struct name : ::mp_units::quantity_spec<name, __VA_ARGS__> { \
-  } name
-
-#endif
-
 
 /**
  * @brief A specification of a derived quantity
diff --git a/src/mp-units-core-fmt.cpp b/src/mp-units-core-fmt.cpp
new file mode 100644
index 00000000..8576e7bb
--- /dev/null
+++ b/src/mp-units-core-fmt.cpp
@@ -0,0 +1,13 @@
+module;
+
+#include <mp-units/bits/core-gmf.h>
+#include <mp-units/bits/fmt_hacks.h>
+
+export module mp_units.core_fmt;
+
+export import mp_units.core;
+
+export
+{
+#include <mp-units/format.h>
+}
diff --git a/src/mp-units-core-io.cpp b/src/mp-units-core-io.cpp
new file mode 100644
index 00000000..db16a2df
--- /dev/null
+++ b/src/mp-units-core-io.cpp
@@ -0,0 +1,13 @@
+module;
+
+#include <mp-units/bits/core-gmf.h>
+#include <sstream>
+
+export module mp_units.core_io;
+
+export import mp_units.core;
+
+export
+{
+#include <mp-units/ostream.h>
+}
diff --git a/src/mp-units-core.cpp b/src/mp-units-core.cpp
new file mode 100644
index 00000000..b0ddbb81
--- /dev/null
+++ b/src/mp-units-core.cpp
@@ -0,0 +1,11 @@
+module;
+
+#include <mp-units/bits/core-gmf.h>
+
+export module mp_units.core;
+
+export
+{
+// core
+#include <mp-units/core.h>
+}
diff --git a/src/mp-units-systems.cpp b/src/mp-units-systems.cpp
new file mode 100644
index 00000000..250bd9eb
--- /dev/null
+++ b/src/mp-units-systems.cpp
@@ -0,0 +1,32 @@
+module;
+
+#include <mp-units/bits/core-gmf.h>
+#include <mp-units/quantity_spec_macro.h>
+
+export module mp_units.systems;
+
+export import mp_units.core;
+
+export
+{
+// systems
+#include <mp-units/systems/angular/angular.h>
+#include <mp-units/systems/cgs/cgs.h>
+#include <mp-units/systems/hep/hep.h>
+#include <mp-units/systems/iau/iau.h>
+#include <mp-units/systems/iec80000/iec80000.h>
+#include <mp-units/systems/imperial/imperial.h>
+#include <mp-units/systems/international/international.h>
+#include <mp-units/systems/isq/isq.h>
+#include <mp-units/systems/isq_angle/isq_angle.h>
+#include <mp-units/systems/natural/natural.h>
+#include <mp-units/systems/si/si.h>
+#include <mp-units/systems/typographic/typographic.h>
+#include <mp-units/systems/usc/usc.h>
+
+// utility
+#include <mp-units/chrono.h>
+#include <mp-units/compare.h>
+#include <mp-units/math.h>
+#include <mp-units/random.h>
+}
diff --git a/src/mp-units.cpp b/src/mp-units.cpp
new file mode 100644
index 00000000..30218060
--- /dev/null
+++ b/src/mp-units.cpp
@@ -0,0 +1,8 @@
+module;
+
+export module mp_units;
+
+export import mp_units.core;
+export import mp_units.core_fmt;
+export import mp_units.core_io;
+export import mp_units.systems;
diff --git a/src/utility/include/mp-units/math.h b/src/utility/include/mp-units/math.h
index 0a37935d..c8d9dce2 100644
--- a/src/utility/include/mp-units/math.h
+++ b/src/utility/include/mp-units/math.h
@@ -29,5 +29,5 @@
 // This header is intentionally empty and just include other headers
 // `math.h` is just a convenience wrapper for not modular code
 // With C++20 modules:
-// - math_core will be a part of the mp_units.core module
-// - math_si and math_angular will be provided with the mp_units.systems module
+// - math_core is be a part of the mp_units.core module
+// - math_si and math_angular is provided with the mp_units.systems module
diff --git a/test/unit_test/runtime/CMakeLists.txt b/test/unit_test/runtime/CMakeLists.txt
index 29846ad2..21686ab5 100644
--- a/test/unit_test/runtime/CMakeLists.txt
+++ b/test/unit_test/runtime/CMakeLists.txt
@@ -25,7 +25,12 @@ cmake_minimum_required(VERSION 3.5)
 find_package(Catch2 3 CONFIG REQUIRED)
 
 add_executable(unit_tests_runtime distribution_test.cpp fmt_test.cpp math_test.cpp)
-target_link_libraries(unit_tests_runtime PRIVATE mp-units::mp-units Catch2::Catch2WithMain)
+if(TARGET mp-units::modules)
+    target_link_libraries(unit_tests_runtime PRIVATE mp-units::modules)
+else()
+    target_link_libraries(unit_tests_runtime PRIVATE mp-units::mp-units)
+endif()
+target_link_libraries(unit_tests_runtime PRIVATE Catch2::Catch2WithMain)
 
 if(${projectPrefix}BUILD_LA)
     find_package(wg21_linear_algebra CONFIG REQUIRED)
diff --git a/test/unit_test/runtime/almost_equals.h b/test/unit_test/runtime/almost_equals.h
index 264182f3..8a871fe9 100644
--- a/test/unit_test/runtime/almost_equals.h
+++ b/test/unit_test/runtime/almost_equals.h
@@ -21,9 +21,14 @@
 // SOFTWARE.
 
 #include <catch2/matchers/catch_matchers_templated.hpp>
+#include <mp-units/bits/fmt_hacks.h>
+#include <algorithm>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/format.h>
 #include <mp-units/quantity.h>
-#include <algorithm>
+#endif
 
 namespace mp_units {
 
diff --git a/test/unit_test/runtime/distribution_test.cpp b/test/unit_test/runtime/distribution_test.cpp
index 5b14ae7f..d3786989 100644
--- a/test/unit_test/runtime/distribution_test.cpp
+++ b/test/unit_test/runtime/distribution_test.cpp
@@ -21,14 +21,18 @@
 // SOFTWARE.
 
 #include <catch2/catch_test_macros.hpp>
-#include <mp-units/ostream.h>
-#include <mp-units/random.h>
-#include <mp-units/systems/si/unit_symbols.h>
-#include <mp-units/systems/si/units.h>
 #include <array>
 #include <initializer_list>
 #include <random>
 #include <vector>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
+#include <mp-units/ostream.h>
+#include <mp-units/random.h>
+#include <mp-units/systems/si/unit_symbols.h>
+#include <mp-units/systems/si/units.h>
+#endif
 
 
 using namespace mp_units;
diff --git a/test/unit_test/runtime/fmt_test.cpp b/test/unit_test/runtime/fmt_test.cpp
index bda7b936..482838b4 100644
--- a/test/unit_test/runtime/fmt_test.cpp
+++ b/test/unit_test/runtime/fmt_test.cpp
@@ -22,6 +22,13 @@
 
 #include <catch2/catch_test_macros.hpp>
 #include <catch2/matchers/catch_matchers_exception.hpp>
+#include <mp-units/bits/fmt_hacks.h>
+#include <iomanip>
+#include <limits>
+#include <locale>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/customization_points.h>
 #include <mp-units/format.h>
 #include <mp-units/ostream.h>
@@ -29,9 +36,7 @@
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/si.h>
-#include <iomanip>
-#include <limits>
-#include <locale>
+#endif
 
 template<class T>
   requires mp_units::is_scalar<T>
diff --git a/test/unit_test/runtime/linear_algebra_test.cpp b/test/unit_test/runtime/linear_algebra_test.cpp
index 492e3bf8..4e227728 100644
--- a/test/unit_test/runtime/linear_algebra_test.cpp
+++ b/test/unit_test/runtime/linear_algebra_test.cpp
@@ -21,6 +21,12 @@
 // SOFTWARE.
 
 #include <catch2/catch_test_macros.hpp>
+#include <mp-units/bits/fmt_hacks.h>
+#include <cmath>
+#include <matrix>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/customization_points.h>
 #include <mp-units/format.h>
 #include <mp-units/math.h>
@@ -28,8 +34,7 @@
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/si.h>
-#include <cmath>
-#include <matrix>
+#endif
 
 template<typename Rep = double>
 using vector = STD_LA::fixed_size_column_vector<Rep, 3>;
diff --git a/test/unit_test/runtime/math_test.cpp b/test/unit_test/runtime/math_test.cpp
index 47e78d74..c6dcc589 100644
--- a/test/unit_test/runtime/math_test.cpp
+++ b/test/unit_test/runtime/math_test.cpp
@@ -22,13 +22,17 @@
 
 #include "almost_equals.h"
 #include <catch2/catch_all.hpp>
+#include <limits>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/math.h>
 #include <mp-units/ostream.h>
 #include <mp-units/systems/angular/angular.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/unit_symbols.h>
 #include <mp-units/systems/si/units.h>
-#include <limits>
+#endif
 
 using namespace mp_units;
 using namespace mp_units::si::unit_symbols;
diff --git a/test/unit_test/static/CMakeLists.txt b/test/unit_test/static/CMakeLists.txt
index 09e09ffd..37cb00c7 100644
--- a/test/unit_test/static/CMakeLists.txt
+++ b/test/unit_test/static/CMakeLists.txt
@@ -23,7 +23,11 @@
 cmake_minimum_required(VERSION 3.5)
 
 add_library(unit_tests_static_truncating quantity_test.cpp)
-target_link_libraries(unit_tests_static_truncating PRIVATE mp-units::mp-units)
+if(TARGET mp-units::modules)
+    target_link_libraries(unit_tests_static_truncating PRIVATE mp-units::modules)
+else()
+    target_link_libraries(unit_tests_static_truncating PRIVATE mp-units::mp-units)
+endif()
 target_compile_options(
     unit_tests_static_truncating PRIVATE $<IF:$<CXX_COMPILER_ID:MSVC>,/wd4242 /wd4244,-Wno-conversion>
 )
@@ -64,5 +68,9 @@ add_library(
     usc_test.cpp
 )
 
-target_link_libraries(unit_tests_static PRIVATE mp-units::mp-units)
-target_link_libraries(unit_tests_static PRIVATE unit_tests_static_truncating mp-units::mp-units)
+if(TARGET mp-units::modules)
+    target_link_libraries(unit_tests_static PRIVATE mp-units::modules)
+else()
+    target_link_libraries(unit_tests_static PRIVATE mp-units::mp-units)
+endif()
+target_link_libraries(unit_tests_static PRIVATE unit_tests_static_truncating)
diff --git a/test/unit_test/static/angular_test.cpp b/test/unit_test/static/angular_test.cpp
index c3010dfe..c0c5a23b 100644
--- a/test/unit_test/static/angular_test.cpp
+++ b/test/unit_test/static/angular_test.cpp
@@ -20,8 +20,12 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#include <mp-units/systems/isq_angle/isq_angle.h>
 #include <numbers>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
+#include <mp-units/systems/isq_angle/isq_angle.h>
+#endif
 
 namespace {
 
diff --git a/test/unit_test/static/cgs_test.cpp b/test/unit_test/static/cgs_test.cpp
index c58c5885..2d2bbf0c 100644
--- a/test/unit_test/static/cgs_test.cpp
+++ b/test/unit_test/static/cgs_test.cpp
@@ -21,10 +21,14 @@
 // SOFTWARE.
 
 #include "test_tools.h"
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/systems/cgs/cgs.h>
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/unit_symbols.h>
+#endif
 
 template<class T>
   requires mp_units::is_scalar<T>
diff --git a/test/unit_test/static/chrono_test.cpp b/test/unit_test/static/chrono_test.cpp
index b8c61fa5..df5fa356 100644
--- a/test/unit_test/static/chrono_test.cpp
+++ b/test/unit_test/static/chrono_test.cpp
@@ -21,11 +21,16 @@
 // SOFTWARE.
 
 #include "test_tools.h"
+#include <ratio>
+#ifdef MP_UNITS_MODULES
+#include <chrono>
+import mp_units;
+#else
 #include <mp-units/bits/external/type_traits.h>
 #include <mp-units/chrono.h>
 #include <mp-units/quantity_point.h>
 #include <mp-units/systems/si/unit_symbols.h>
-#include <ratio>
+#endif
 
 namespace {
 
diff --git a/test/unit_test/static/compare_test.cpp b/test/unit_test/static/compare_test.cpp
index 5de812d9..6c966f19 100644
--- a/test/unit_test/static/compare_test.cpp
+++ b/test/unit_test/static/compare_test.cpp
@@ -20,8 +20,12 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/compare.h>
 #include <mp-units/systems/si/si.h>
+#endif
 
 namespace {
 
diff --git a/test/unit_test/static/concepts_test.cpp b/test/unit_test/static/concepts_test.cpp
index 4312e638..2c050f8b 100644
--- a/test/unit_test/static/concepts_test.cpp
+++ b/test/unit_test/static/concepts_test.cpp
@@ -20,16 +20,20 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#include <chrono>
+#include <complex>
+#include <optional>
+#include <string>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/chrono.h>
 #include <mp-units/concepts.h>
 #include <mp-units/quantity_point.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/natural/natural.h>
 #include <mp-units/systems/si/si.h>
-#include <chrono>
-#include <complex>
-#include <optional>
-#include <string>
+#endif
 
 template<typename T>
 inline constexpr bool mp_units::is_scalar<std::complex<T>> = true;
diff --git a/test/unit_test/static/custom_rep_test_min_expl.cpp b/test/unit_test/static/custom_rep_test_min_expl.cpp
index 689c9666..9288679d 100644
--- a/test/unit_test/static/custom_rep_test_min_expl.cpp
+++ b/test/unit_test/static/custom_rep_test_min_expl.cpp
@@ -20,11 +20,15 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#include <ostream>
+#include <type_traits>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <units/generic/dimensionless.h>
 #include <units/isq/si/length.h>
 #include <units/isq/si/prefixes.h>
-#include <ostream>
-#include <type_traits>
+#endif
 
 namespace {
 
diff --git a/test/unit_test/static/custom_rep_test_min_impl.cpp b/test/unit_test/static/custom_rep_test_min_impl.cpp
index 7d18effd..2ebc01a6 100644
--- a/test/unit_test/static/custom_rep_test_min_impl.cpp
+++ b/test/unit_test/static/custom_rep_test_min_impl.cpp
@@ -20,8 +20,14 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#include <mp-units/systems/si/units.h>
+#include <mp-units/bits/external/hacks.h>
+#include <concepts>
 #include <type_traits>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
+#include <mp-units/systems/si/units.h>
+#endif
 
 namespace {
 
diff --git a/test/unit_test/static/dimension_test.cpp b/test/unit_test/static/dimension_test.cpp
index 808620d7..04a95357 100644
--- a/test/unit_test/static/dimension_test.cpp
+++ b/test/unit_test/static/dimension_test.cpp
@@ -21,11 +21,15 @@
 // SOFTWARE.
 
 #include "test_tools.h"
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/dimension.h>
 #include <mp-units/quantity.h>
 #include <mp-units/quantity_spec.h>
 #include <mp-units/reference.h>
 #include <mp-units/unit.h>
+#endif
 
 namespace {
 
diff --git a/test/unit_test/static/fixed_string_test.cpp b/test/unit_test/static/fixed_string_test.cpp
index 4835fbdf..c4a56aed 100644
--- a/test/unit_test/static/fixed_string_test.cpp
+++ b/test/unit_test/static/fixed_string_test.cpp
@@ -20,7 +20,11 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/bits/external/fixed_string.h>
+#endif
 
 using namespace mp_units;
 
diff --git a/test/unit_test/static/fractional_exponent_quantity.cpp b/test/unit_test/static/fractional_exponent_quantity.cpp
index d8a1b513..6014b34e 100644
--- a/test/unit_test/static/fractional_exponent_quantity.cpp
+++ b/test/unit_test/static/fractional_exponent_quantity.cpp
@@ -20,9 +20,14 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#include <mp-units/quantity_spec_macro.h>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/math.h>
 #include <mp-units/systems/isq/electromagnetism.h>
 #include <mp-units/systems/si/units.h>
+#endif
 
 namespace {
 
diff --git a/test/unit_test/static/hep_test.cpp b/test/unit_test/static/hep_test.cpp
index 93a95321..d5e2384a 100644
--- a/test/unit_test/static/hep_test.cpp
+++ b/test/unit_test/static/hep_test.cpp
@@ -20,10 +20,14 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/systems/hep/hep.h>
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/si.h>
+#endif
 
 template<class T>
   requires mp_units::is_scalar<T>
diff --git a/test/unit_test/static/iau_test.cpp b/test/unit_test/static/iau_test.cpp
index 6e414b0b..54738538 100644
--- a/test/unit_test/static/iau_test.cpp
+++ b/test/unit_test/static/iau_test.cpp
@@ -20,9 +20,13 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/math.h>
 #include <mp-units/systems/iau/iau.h>
 #include <mp-units/systems/si/unit_symbols.h>
+#endif
 
 /* ************** DERIVED DIMENSIONS THAT INCLUDE UNITS WITH SPECIAL NAMES **************** */
 
diff --git a/test/unit_test/static/iec80000_test.cpp b/test/unit_test/static/iec80000_test.cpp
index 2718758f..1021a6cc 100644
--- a/test/unit_test/static/iec80000_test.cpp
+++ b/test/unit_test/static/iec80000_test.cpp
@@ -20,10 +20,14 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/quantity.h>
 #include <mp-units/reference.h>
 #include <mp-units/systems/iec80000/iec80000.h>
 #include <mp-units/systems/si/unit_symbols.h>
+#endif
 
 /* ************** DERIVED DIMENSIONS THAT INCLUDE UNITS WITH SPECIAL NAMES **************** */
 
diff --git a/test/unit_test/static/imperial_test.cpp b/test/unit_test/static/imperial_test.cpp
index 7b3b3a74..13d1ed26 100644
--- a/test/unit_test/static/imperial_test.cpp
+++ b/test/unit_test/static/imperial_test.cpp
@@ -20,9 +20,13 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/systems/imperial/imperial.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/unit_symbols.h>
+#endif
 
 namespace {
 
diff --git a/test/unit_test/static/international_test.cpp b/test/unit_test/static/international_test.cpp
index a5a31219..910c9e26 100644
--- a/test/unit_test/static/international_test.cpp
+++ b/test/unit_test/static/international_test.cpp
@@ -20,12 +20,16 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/math.h>
 #include <mp-units/systems/international/international.h>
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/constants.h>
 #include <mp-units/systems/si/units.h>
+#endif
 
 template<class T>
   requires mp_units::is_scalar<T>
diff --git a/test/unit_test/static/isq_angle_test.cpp b/test/unit_test/static/isq_angle_test.cpp
index ef597076..fdb32496 100644
--- a/test/unit_test/static/isq_angle_test.cpp
+++ b/test/unit_test/static/isq_angle_test.cpp
@@ -20,8 +20,12 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/systems/isq_angle/isq_angle.h>
 #include <mp-units/systems/si/unit_symbols.h>
+#endif
 
 namespace {
 
diff --git a/test/unit_test/static/isq_test.cpp b/test/unit_test/static/isq_test.cpp
index 4d7333f2..9a67d44e 100644
--- a/test/unit_test/static/isq_test.cpp
+++ b/test/unit_test/static/isq_test.cpp
@@ -20,9 +20,13 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/reference.h>
 #include <mp-units/systems/isq/isq.h>
 #include <mp-units/systems/si/unit_symbols.h>
+#endif
 
 namespace {
 
diff --git a/test/unit_test/static/magnitude_test.cpp b/test/unit_test/static/magnitude_test.cpp
index eaf2cc17..f0eb031b 100644
--- a/test/unit_test/static/magnitude_test.cpp
+++ b/test/unit_test/static/magnitude_test.cpp
@@ -20,9 +20,13 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <units/bits/magnitude.h>
 #include <units/bits/ratio.h>
 #include <type_traits>
+#endif
 
 using namespace units;
 using namespace units::detail;
diff --git a/test/unit_test/static/math_test.cpp b/test/unit_test/static/math_test.cpp
index 528ea206..d4f52037 100644
--- a/test/unit_test/static/math_test.cpp
+++ b/test/unit_test/static/math_test.cpp
@@ -20,11 +20,15 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#include <optional>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/math.h>  // IWYU pragma: keep
 #include <mp-units/systems/international/international.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/unit_symbols.h>
-#include <optional>
+#endif
 
 namespace {
 
diff --git a/test/unit_test/static/natural_test.cpp b/test/unit_test/static/natural_test.cpp
index 7880642b..f24f31e1 100644
--- a/test/unit_test/static/natural_test.cpp
+++ b/test/unit_test/static/natural_test.cpp
@@ -20,8 +20,12 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/math.h>
 #include <mp-units/systems/natural/natural.h>
+#endif
 
 template<class T>
   requires mp_units::is_scalar<T>
diff --git a/test/unit_test/static/prime_test.cpp b/test/unit_test/static/prime_test.cpp
index 0fd724bd..d6647a10 100644
--- a/test/unit_test/static/prime_test.cpp
+++ b/test/unit_test/static/prime_test.cpp
@@ -20,9 +20,13 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#include <mp-units/bits/external/prime.h>
 #include <type_traits>
 #include <utility>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
+#include <mp-units/bits/external/prime.h>
+#endif
 
 using namespace mp_units::detail;
 
diff --git a/test/unit_test/static/quantity_point_test.cpp b/test/unit_test/static/quantity_point_test.cpp
index 4ebfb5ad..b44da9f0 100644
--- a/test/unit_test/static/quantity_point_test.cpp
+++ b/test/unit_test/static/quantity_point_test.cpp
@@ -21,14 +21,19 @@
 // SOFTWARE.
 
 #include "test_tools.h"
+#include <limits>
+#include <type_traits>
+#include <utility>
+#ifdef MP_UNITS_MODULES
+#include <chrono>
+import mp_units;
+#else
 #include <mp-units/chrono.h>
 #include <mp-units/quantity_point.h>
 #include <mp-units/systems/isq/isq.h>
 #include <mp-units/systems/si/si.h>
 #include <mp-units/systems/usc/usc.h>
-#include <limits>
-#include <type_traits>
-#include <utility>
+#endif
 
 namespace {
 
diff --git a/test/unit_test/static/quantity_spec_test.cpp b/test/unit_test/static/quantity_spec_test.cpp
index ab7694c1..d9713686 100644
--- a/test/unit_test/static/quantity_spec_test.cpp
+++ b/test/unit_test/static/quantity_spec_test.cpp
@@ -21,10 +21,14 @@
 // SOFTWARE.
 
 #include "test_tools.h"
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/quantity.h>
 #include <mp-units/quantity_spec.h>
 #include <mp-units/reference.h>
 #include <mp-units/unit.h>
+#endif
 
 namespace {
 
diff --git a/test/unit_test/static/quantity_test.cpp b/test/unit_test/static/quantity_test.cpp
index 47ed833c..11721955 100644
--- a/test/unit_test/static/quantity_test.cpp
+++ b/test/unit_test/static/quantity_test.cpp
@@ -21,12 +21,17 @@
 // SOFTWARE.
 
 #include "test_tools.h"
+#include <limits>
+#include <utility>
+#ifdef MP_UNITS_MODULES
+#include <chrono>
+import mp_units;
+#else
 #include <mp-units/chrono.h>
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/si.h>
-#include <limits>
-#include <utility>
+#endif
 
 template<>
 inline constexpr bool mp_units::is_vector<int> = true;
diff --git a/test/unit_test/static/ratio_test.cpp b/test/unit_test/static/ratio_test.cpp
index 5bf9bec0..fd2113bc 100644
--- a/test/unit_test/static/ratio_test.cpp
+++ b/test/unit_test/static/ratio_test.cpp
@@ -20,7 +20,11 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/bits/ratio.h>
+#endif
 
 namespace {
 
diff --git a/test/unit_test/static/reference_test.cpp b/test/unit_test/static/reference_test.cpp
index 3aac7e59..8da7fa48 100644
--- a/test/unit_test/static/reference_test.cpp
+++ b/test/unit_test/static/reference_test.cpp
@@ -21,6 +21,9 @@
 // SOFTWARE.
 
 #include "test_tools.h"
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/dimension.h>
 #include <mp-units/quantity.h>
 #include <mp-units/quantity_spec.h>
@@ -28,6 +31,7 @@
 #include <mp-units/system_reference.h>
 #include <mp-units/systems/si/prefixes.h>
 #include <mp-units/unit.h>
+#endif
 
 namespace {
 
diff --git a/test/unit_test/static/si_test.cpp b/test/unit_test/static/si_test.cpp
index 69d83096..8ce65935 100644
--- a/test/unit_test/static/si_test.cpp
+++ b/test/unit_test/static/si_test.cpp
@@ -20,8 +20,13 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#include <type_traits>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/math.h>
 #include <mp-units/systems/si/si.h>
+#endif
 
 namespace {
 
diff --git a/test/unit_test/static/symbol_text_test.cpp b/test/unit_test/static/symbol_text_test.cpp
index 1eb4700b..950c39e6 100644
--- a/test/unit_test/static/symbol_text_test.cpp
+++ b/test/unit_test/static/symbol_text_test.cpp
@@ -20,7 +20,11 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/bits/symbol_text.h>
+#endif
 
 using namespace mp_units;
 
diff --git a/test/unit_test/static/test_tools.h b/test/unit_test/static/test_tools.h
index 42cbc61e..bf6f77a5 100644
--- a/test/unit_test/static/test_tools.h
+++ b/test/unit_test/static/test_tools.h
@@ -22,8 +22,13 @@
 
 #pragma once
 
-#include <mp-units/quantity_spec.h>
 #include <type_traits>
+#ifdef MP_UNITS_MODULES
+#include <mp-units/quantity_spec_macro.h>
+import mp_units;
+#else
+#include <mp-units/quantity_spec.h>
+#endif
 
 template<auto V, typename T>
 inline constexpr bool is_of_type = std::is_same_v<std::remove_cvref_t<decltype(V)>, T>;
diff --git a/test/unit_test/static/type_list_test.cpp b/test/unit_test/static/type_list_test.cpp
index 6720ebbb..c3d61d52 100644
--- a/test/unit_test/static/type_list_test.cpp
+++ b/test/unit_test/static/type_list_test.cpp
@@ -20,8 +20,13 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#include <type_traits>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/bits/external/type_list.h>
 #include <mp-units/bits/external/type_traits.h>
+#endif
 
 namespace {
 
diff --git a/test/unit_test/static/typographic_test.cpp b/test/unit_test/static/typographic_test.cpp
index 9a47469c..71c713d1 100644
--- a/test/unit_test/static/typographic_test.cpp
+++ b/test/unit_test/static/typographic_test.cpp
@@ -20,9 +20,13 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/systems/international/international.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/typographic/typographic.h>
+#endif
 
 namespace {
 
diff --git a/test/unit_test/static/unit_symbol_test.cpp b/test/unit_test/static/unit_symbol_test.cpp
index d5a41358..24fe56fa 100644
--- a/test/unit_test/static/unit_symbol_test.cpp
+++ b/test/unit_test/static/unit_symbol_test.cpp
@@ -20,9 +20,13 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/systems/iau/iau.h>
 #include <mp-units/systems/iec80000/iec80000.h>
 #include <mp-units/systems/si/si.h>
+#endif
 
 namespace {
 
diff --git a/test/unit_test/static/unit_test.cpp b/test/unit_test/static/unit_test.cpp
index ca4ae1cc..d187467a 100644
--- a/test/unit_test/static/unit_test.cpp
+++ b/test/unit_test/static/unit_test.cpp
@@ -21,11 +21,15 @@
 // SOFTWARE.
 
 #include "test_tools.h"
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/dimension.h>
 #include <mp-units/quantity.h>
 #include <mp-units/reference.h>
 #include <mp-units/systems/si/prefixes.h>
 #include <mp-units/unit.h>
+#endif
 
 namespace {
 
diff --git a/test/unit_test/static/usc_test.cpp b/test/unit_test/static/usc_test.cpp
index c4e35e9e..42c29389 100644
--- a/test/unit_test/static/usc_test.cpp
+++ b/test/unit_test/static/usc_test.cpp
@@ -20,10 +20,15 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#include <mp-units/bits/external/hacks.h>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/unit_symbols.h>
 #include <mp-units/systems/usc/usc.h>
+#endif
 
 namespace {