diff --git a/bench/bench_set.hpp b/bench/bench_set.hpp
index 4af500c..46ca9dd 100644
--- a/bench/bench_set.hpp
+++ b/bench/bench_set.hpp
@@ -471,7 +471,7 @@ void launch_tests(const char *BoostContName, const char *StdContName)
          extensions_time< BoostClass >(get_range_t::sorted_unique());
       }
 
-   }catch(std::exception e){
+   }catch(std::exception &e){
       std::cout << e.what();
    }
 }
diff --git a/bench/bench_static_vector.cpp b/bench/bench_static_vector.cpp
index 4553dc7..d9dd8a7 100644
--- a/bench/bench_static_vector.cpp
+++ b/bench/bench_static_vector.cpp
@@ -137,7 +137,7 @@ int main()
 
       std::cout << "varray/std::vector total time comparison:";
       compare_times(time_varray,time_standard_vector);
-   }catch(std::exception e){
+   }catch(std::exception &e){
       std::cout << e.what();
    }
    return 0;
diff --git a/doc/container.qbk b/doc/container.qbk
index 4f8ea7f..93ab8a1 100644
--- a/doc/container.qbk
+++ b/doc/container.qbk
@@ -1240,6 +1240,16 @@ use [*Boost.Container]? There are several reasons for that:
 
 [section:release_notes Release Notes]
 
+[section:release_notes_boost_1_69_00 Boost 1.69 Release]
+
+* Implemented C++20 `contains()` for associative containers as specified in
+   [@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0458r2.html
+   P0458R2: Checking for Existence of an Element in Associative Containers].
+
+* Fixed serious bug in heterogeneous lookup functions (is_transparent was broken).
+
+[endsect]
+
 [section:release_notes_boost_1_68_00 Boost 1.68 Release]
 
 * Improved correctness of [classref boost::container::adaptive_pool adaptive_pool] and many parameters are now compile-time
diff --git a/include/boost/container/detail/flat_tree.hpp b/include/boost/container/detail/flat_tree.hpp
index e9cbe38..061b840 100644
--- a/include/boost/container/detail/flat_tree.hpp
+++ b/include/boost/container/detail/flat_tree.hpp
@@ -1201,6 +1201,15 @@ class flat_tree
       return n;
    }
 
+   BOOST_CONTAINER_FORCEINLINE bool contains(const key_type& x) const
+   {  return this->find(x) != this->cend();  }
+
+   template<typename K>
+   BOOST_CONTAINER_FORCEINLINE
+      typename dtl::enable_if_transparent<key_compare, K, bool>::type
+         contains(const K& x) const
+   {  return this->find(x) != this->cend();  }
+
    template<class C2>
    BOOST_CONTAINER_FORCEINLINE void merge_unique(flat_tree<Value, KeyOfValue, C2, AllocatorOrContainer>& source)
    {
diff --git a/include/boost/container/detail/mpl.hpp b/include/boost/container/detail/mpl.hpp
index 385f7db..5249dbf 100644
--- a/include/boost/container/detail/mpl.hpp
+++ b/include/boost/container/detail/mpl.hpp
@@ -76,19 +76,28 @@ struct select1st
    {  return const_cast<type&>(x.first);   }
 };
 
+
+template<typename T>
+struct void_t { typedef void type; };
+
 template <class T, class=void>
-struct is_transparent
+struct is_transparent_base
 {
    static const bool value = false;
 };
 
 template <class T>
-struct is_transparent<T, typename T::is_transparent>
+struct is_transparent_base<T, typename void_t<typename T::is_transparent>::type>
 {
    static const bool value = true;
 };
 
-template <typename C, typename K, typename R>
+template <class T>
+struct is_transparent
+   : is_transparent_base<T>
+{};
+
+template <typename C, class /*Dummy*/, typename R>
 struct enable_if_transparent
    : boost::move_detail::enable_if_c<dtl::is_transparent<C>::value, R>
 {};
diff --git a/include/boost/container/detail/tree.hpp b/include/boost/container/detail/tree.hpp
index c32e992..7d02553 100644
--- a/include/boost/container/detail/tree.hpp
+++ b/include/boost/container/detail/tree.hpp
@@ -1297,6 +1297,15 @@ class tree
          count(const K& k) const
    {  return size_type(this->icont().count(k, KeyNodeCompare(key_comp()))); }
 
+   BOOST_CONTAINER_FORCEINLINE bool contains(const key_type& x) const
+   {  return this->find(x) != this->cend();  }
+
+   template<typename K>
+   BOOST_CONTAINER_FORCEINLINE
+      typename dtl::enable_if_transparent<key_compare, K, bool>::type
+         contains(const K& x) const
+   {  return this->find(x) != this->cend();  }
+
    BOOST_CONTAINER_FORCEINLINE iterator lower_bound(const key_type& k)
    {  return iterator(this->icont().lower_bound(k, KeyNodeCompare(key_comp())));  }
 
diff --git a/include/boost/container/flat_map.hpp b/include/boost/container/flat_map.hpp
index 9679946..191f3b9 100644
--- a/include/boost/container/flat_map.hpp
+++ b/include/boost/container/flat_map.hpp
@@ -1340,6 +1340,24 @@ class flat_map
    BOOST_CONTAINER_FORCEINLINE size_type count(const K& x) const
       {  return static_cast<size_type>(m_flat_tree.find(x) != m_flat_tree.end());  }
 
+   //! <b>Returns</b>: Returns true if there is an element with key
+   //!   equivalent to key in the container, otherwise false.
+   //!
+   //! <b>Complexity</b>: log(size()).
+   bool contains(const key_type& x) const
+      {  return m_flat_tree.find(x) != m_flat_tree.end();  }
+
+   //! <b>Requires</b>: This overload is available only if
+   //! key_compare::is_transparent exists.
+   //!
+   //! <b>Returns</b>: Returns true if there is an element with key
+   //!   equivalent to key in the container, otherwise false.
+   //!
+   //! <b>Complexity</b>: log(size()).
+   template<typename K>
+   bool contains(const K& x) const
+      {  return m_flat_tree.find(x) != m_flat_tree.end();  }
+
    //! <b>Returns</b>: An iterator pointing to the first element with key not less
    //!   than k, or a.end() if such an element is not found.
    //!
@@ -2631,6 +2649,24 @@ class flat_multimap
    BOOST_CONTAINER_FORCEINLINE size_type count(const K& x) const
       { return m_flat_tree.count(x); }
 
+   //! <b>Returns</b>: Returns true if there is an element with key
+   //!   equivalent to key in the container, otherwise false.
+   //!
+   //! <b>Complexity</b>: log(size()).
+   bool contains(const key_type& x) const
+      {  return m_flat_tree.find(x) != m_flat_tree.end();  }
+
+   //! <b>Requires</b>: This overload is available only if
+   //! key_compare::is_transparent exists.
+   //!
+   //! <b>Returns</b>: Returns true if there is an element with key
+   //!   equivalent to key in the container, otherwise false.
+   //!
+   //! <b>Complexity</b>: log(size()).
+   template<typename K>
+   bool contains(const K& x) const
+      {  return m_flat_tree.find(x) != m_flat_tree.end();  }
+
    //! <b>Returns</b>: An iterator pointing to the first element with key not less
    //!   than k, or a.end() if such an element is not found.
    //!
diff --git a/include/boost/container/flat_set.hpp b/include/boost/container/flat_set.hpp
index cfea7c8..c4dd827 100644
--- a/include/boost/container/flat_set.hpp
+++ b/include/boost/container/flat_set.hpp
@@ -912,6 +912,23 @@ class flat_set
    {  return static_cast<size_type>(this->tree_t::find(x) != this->tree_t::cend());  }
 
    #if defined(BOOST_CONTAINER_DOXYGEN_INVOKED)
+
+   //! <b>Returns</b>: Returns true if there is an element with key
+   //!   equivalent to key in the container, otherwise false.
+   //!
+   //! <b>Complexity</b>: log(size()).
+   bool contains(const key_type& x) const;
+
+   //! <b>Requires</b>: This overload is available only if
+   //! key_compare::is_transparent exists.
+   //!
+   //! <b>Returns</b>: Returns true if there is an element with key
+   //!   equivalent to key in the container, otherwise false.
+   //!
+   //! <b>Complexity</b>: log(size()).
+   template<typename K>
+   bool contains(const K& x) const;
+
    //! <b>Returns</b>: An iterator pointing to the first element with key not less
    //!   than k, or a.end() if such an element is not found.
    //!
@@ -1685,6 +1702,13 @@ class flat_multiset
    //! @copydoc ::boost::container::flat_set::count(const key_type& ) const
    size_type count(const key_type& x) const;
 
+   //! @copydoc ::boost::container::flat_set::contains(const key_type& ) const
+   bool contains(const key_type& x) const;
+
+   //! @copydoc ::boost::container::flat_set::contains(const K& ) const
+   template<typename K>
+   bool contains(const K& x) const;
+
    //! @copydoc ::boost::container::flat_set::lower_bound(const key_type& )
    iterator lower_bound(const key_type& x);
 
diff --git a/include/boost/container/map.hpp b/include/boost/container/map.hpp
index a88b6a5..02bd74f 100644
--- a/include/boost/container/map.hpp
+++ b/include/boost/container/map.hpp
@@ -1119,6 +1119,22 @@ class map
 
    #if defined(BOOST_CONTAINER_DOXYGEN_INVOKED)
 
+   //! <b>Returns</b>: Returns true if there is an element with key
+   //!   equivalent to key in the container, otherwise false.
+   //!
+   //! <b>Complexity</b>: log(size()).
+   bool contains(const key_type& x) const;
+
+   //! <b>Requires</b>: This overload is available only if
+   //! key_compare::is_transparent exists.
+   //!
+   //! <b>Returns</b>: Returns true if there is an element with key
+   //!   equivalent to key in the container, otherwise false.
+   //!
+   //! <b>Complexity</b>: log(size()).
+   template<typename K>
+   bool contains(const K& x) const;
+
    //! <b>Returns</b>: An iterator pointing to the first element with key not less
    //!   than k, or a.end() if such an element is not found.
    //!
@@ -2017,6 +2033,22 @@ class multimap
    template<typename K>
    size_type count(const K& x) const;
 
+   //! <b>Returns</b>: Returns true if there is an element with key
+   //!   equivalent to key in the container, otherwise false.
+   //!
+   //! <b>Complexity</b>: log(size()).
+   bool contains(const key_type& x) const;
+
+   //! <b>Requires</b>: This overload is available only if
+   //! key_compare::is_transparent exists.
+   //!
+   //! <b>Returns</b>: Returns true if there is an element with key
+   //!   equivalent to key in the container, otherwise false.
+   //!
+   //! <b>Complexity</b>: log(size()).
+   template<typename K>
+   bool contains(const K& x) const;
+
    //! <b>Returns</b>: An iterator pointing to the first element with key not less
    //!   than k, or a.end() if such an element is not found.
    //!
diff --git a/include/boost/container/set.hpp b/include/boost/container/set.hpp
index e300898..68425be 100644
--- a/include/boost/container/set.hpp
+++ b/include/boost/container/set.hpp
@@ -772,14 +772,24 @@ class set
    BOOST_CONTAINER_FORCEINLINE size_type count(const K& x) const
    {  return static_cast<size_type>(this->find(x) != this->cend());  }
 
-   //! <b>Returns</b>: The number of elements with key equivalent to x.
-   //!
-   //! <b>Complexity</b>: log(size())+count(k)
-   BOOST_CONTAINER_FORCEINLINE size_type count(const key_type& x)
-   {  return static_cast<size_type>(this->base_t::find(x) != this->base_t::end());  }
-
    #if defined(BOOST_CONTAINER_DOXYGEN_INVOKED)
 
+   //! <b>Returns</b>: Returns true if there is an element with key
+   //!   equivalent to key in the container, otherwise false.
+   //!
+   //! <b>Complexity</b>: log(size()).
+   bool contains(const key_type& x) const;
+
+   //! <b>Requires</b>: This overload is available only if
+   //! key_compare::is_transparent exists.
+   //!
+   //! <b>Returns</b>: Returns true if there is an element with key
+   //!   equivalent to key in the container, otherwise false.
+   //!
+   //! <b>Complexity</b>: log(size()).
+   template<typename K>
+   bool contains(const K& x) const;
+
    //! <b>Returns</b>: An iterator pointing to the first element with key not less
    //!   than k, or a.end() if such an element is not found.
    //!
@@ -1461,6 +1471,13 @@ class multiset
    template<typename K>
    size_type count(const K& x) const;
 
+   //! @copydoc ::boost::container::set::contains(const key_type& ) const
+   bool contains(const key_type& x) const;
+
+   //! @copydoc ::boost::container::set::contains(const K& ) const
+   template<typename K>
+   bool contains(const K& x) const;
+
    //! @copydoc ::boost::container::set::lower_bound(const key_type& )
    iterator lower_bound(const key_type& x);
 
diff --git a/test/flat_map_test.cpp b/test/flat_map_test.cpp
index 7a9a3e7..8118591 100644
--- a/test/flat_map_test.cpp
+++ b/test/flat_map_test.cpp
@@ -454,6 +454,8 @@ struct get_real_stored_allocator<flat_multimap<Key, T, Compare, Allocator> >
 
 bool test_heterogeneous_lookups()
 {
+   BOOST_STATIC_ASSERT((dtl::is_transparent<less_transparent>::value));
+   BOOST_STATIC_ASSERT(!(dtl::is_transparent<std::less<int> >::value));
    typedef flat_map<int, char, less_transparent> map_t;
    typedef flat_multimap<int, char, less_transparent> mmap_t;
    typedef map_t::value_type value_type;
@@ -498,6 +500,16 @@ bool test_heterogeneous_lookups()
    if(cmmap1.count(find_me) != 2)
       return false;
 
+   //contains
+   if(!map1.contains(find_me))
+      return false;
+   if(!cmap1.contains(find_me))
+      return false;
+   if(!mmap1.contains(find_me))
+      return false;
+   if(!cmmap1.contains(find_me))
+      return false;
+
    //lower_bound
    if(map1.lower_bound(find_me)->second != 'd')
       return false;
@@ -709,4 +721,3 @@ int main()
 }
 
 #include <boost/container/detail/config_end.hpp>
-
diff --git a/test/flat_set_test.cpp b/test/flat_set_test.cpp
index fc8233a..e720932 100644
--- a/test/flat_set_test.cpp
+++ b/test/flat_set_test.cpp
@@ -495,6 +495,16 @@ bool test_heterogeneous_lookups()
    if(cmset1.count(find_me) != 2)
       return false;
 
+   //contains
+   if(!set1.contains(find_me))
+      return false;
+   if(!cset1.contains(find_me))
+      return false;
+   if(!mset1.contains(find_me))
+      return false;
+   if(!cmset1.contains(find_me))
+      return false;
+
    //lower_bound
    if(*set1.lower_bound(find_me) != 2)
       return false;
diff --git a/test/map_test.cpp b/test/map_test.cpp
index 619646a..ec4c33e 100644
--- a/test/map_test.cpp
+++ b/test/map_test.cpp
@@ -366,6 +366,16 @@ bool test_heterogeneous_lookups()
    if(cmmap1.count(find_me) != 2)
       return false;
 
+   //contains
+   if(!map1.contains(find_me))
+      return false;
+   if(!cmap1.contains(find_me))
+      return false;
+   if(!mmap1.contains(find_me))
+      return false;
+   if(!cmmap1.contains(find_me))
+      return false;
+
    //lower_bound
    if(map1.lower_bound(find_me)->second != 'd')
       return false;
diff --git a/test/map_test.hpp b/test/map_test.hpp
index 93dbf2f..2ac3efd 100644
--- a/test/map_test.hpp
+++ b/test/map_test.hpp
@@ -628,16 +628,24 @@ int map_test()
          }
       }
 
-      //Compare count with std containers
+      //Compare count/contains with std containers
       for(int i = 0; i < MaxElem; ++i){
          IntType k(i);
          if(boostmap.count(k) != stdmap.count(i)){
             return -1;
          }
 
+         if(boostmap.contains(k) != (stdmap.find(i) != stdmap.end())){
+            return -1;
+         }
+
          if(boostmultimap.count(k) != stdmultimap.count(i)){
             return -1;
          }
+
+         if(boostmultimap.contains(k) != (stdmultimap.find(i) != stdmultimap.end())){
+            return -1;
+         }
       }
 
       //Now do count exercise
diff --git a/test/set_test.cpp b/test/set_test.cpp
index 6fc311d..7a693fc 100644
--- a/test/set_test.cpp
+++ b/test/set_test.cpp
@@ -363,6 +363,16 @@ bool test_heterogeneous_lookups()
    if(cmset1.count(find_me) != 2)
       return false;
 
+   //contains
+   if(!set1.contains(find_me))
+      return false;
+   if(!cset1.contains(find_me))
+      return false;
+   if(!mset1.contains(find_me))
+      return false;
+   if(!cmset1.contains(find_me))
+      return false;
+
    //lower_bound
    if(*set1.lower_bound(find_me) != 2)
       return false;
diff --git a/test/set_test.hpp b/test/set_test.hpp
index b8ca649..c31882a 100644
--- a/test/set_test.hpp
+++ b/test/set_test.hpp
@@ -580,11 +580,20 @@ int set_test ()
 
    //Compare count with std containers
    for(int i = 0; i < MaxElem; ++i){
-      IntType count_me(i);
-      if(boostset.count(count_me) != stdset.count(i)){
+      IntType k(i);
+      if(boostset.count(k) != stdset.count(i)){
          return -1;
       }
-      if(boostmultiset.count(count_me) != stdmultiset.count(i)){
+
+      if(boostset.contains(k) != (stdset.find(i) != stdset.end())){
+         return -1;
+      }
+
+      if(boostmultiset.count(k) != stdmultiset.count(i)){
+         return -1;
+      }
+
+      if(boostmultiset.contains(k) != (stdmultiset.find(i) != stdmultiset.end())){
          return -1;
       }
    }