diff --git a/doc/alignof.qbk b/doc/alignof.qbk
new file mode 100644
index 0000000..13a12f0
--- /dev/null
+++ b/doc/alignof.qbk
@@ -0,0 +1,33 @@
+[/
+  Copyright 2023 Peter Dimov
+  Distributed under the Boost Software License, Version 1.0.
+  https://boost.org/LICENSE_1_0.txt
+]
+
+[section:alignof alignof]
+
+[simplesect Authors]
+
+* Peter Dimov
+
+[endsimplesect]
+
+[section Header <boost/core/alignof.hpp>]
+
+The header `<boost/core/alignof.hpp>` defines the macro `BOOST_CORE_ALIGNOF`,
+a portable equivalent of the `alignof` operator from C++11.
+
+[section Example]
+
+``
+#include <boost/core/alignof.hpp>
+#include <cstddef>
+
+constexpr std::size_t alignment_of_double = BOOST_CORE_ALIGNOF(double);
+``
+
+[endsect]
+
+[endsect]
+
+[endsect]
diff --git a/doc/changes.qbk b/doc/changes.qbk
index b77108a..1826d83 100644
--- a/doc/changes.qbk
+++ b/doc/changes.qbk
@@ -17,6 +17,7 @@
 * Marked `boost::ref` member functions and associated methods with `noexcept`.
 * Marked `boost::swap` function with `noexcept`, depending on whether the type supports a non-throwing swap operation.
 * Added `boost::core::launder`, a portable implementation of `std::launder`.
+* Added `BOOST_CORE_ALIGNOF`, a portable implementation of `alignof`.
 
 [endsect]
 
diff --git a/doc/core.qbk b/doc/core.qbk
index 54b7b66..1cdcb20 100644
--- a/doc/core.qbk
+++ b/doc/core.qbk
@@ -41,6 +41,7 @@ criteria for inclusion is that the utility component be:
 [include changes.qbk]
 
 [include addressof.qbk]
+[include alignof.qbk]
 [include allocator_access.qbk]
 [include allocator_traits.qbk]
 [include bit.qbk]