diff --git a/libcxx/include/type_traits b/libcxx/include/type_traits
--- a/libcxx/include/type_traits
+++ b/libcxx/include/type_traits
@@ -2411,6 +2411,196 @@
 template <class ..._Tp> using common_type_t = typename common_type<_Tp...>::type;
 #endif
 
+// common_reference
+#if _LIBCPP_STD_VER > 17 && defined(__cpp_concepts) && __cpp_concepts >= 201811L
+// Let COND_RES(X, Y) be:
+template <class _Xp, class _Yp>
+using __cond_res =
+    decltype(false ? _VSTD::declval<_Xp(&)()>()() : _VSTD::declval<_Yp(&)()>()());
+
+// Let COPYCV(FROM, TO) be an alias for type TO with the addition of FROM’s
+// top-level cv-qualifiers.
+template <class _From>
+struct __copy_cv_
+{
+    template <class _To>
+    using __res_type = _To;
+};
+template <class _From>
+struct __copy_cv_<const _From>
+{
+    template <class _To>
+    using __res_type = add_const_t<_To>;
+};
+template <class _From>
+struct __copy_cv_<volatile _From>
+{
+    template <class _To>
+    using __res_type = add_volatile_t<_To>;
+};
+template <class _From>
+struct __copy_cv_<const volatile _From>
+{
+    template <class _To>
+    using __res_type = add_cv_t<_To>;
+};
+template <class _From, class _To>
+using __copy_cv = typename __copy_cv_<_From>::template __res_type<_To>;
+
+// Let XREF(A) denote a unary class [sic] template T such [...]
+// [Note: XREF(A) is __xref<A>::template __res_type]
+template <class _Tp>
+struct __xref
+{
+    template <class _Up>
+    using __res_type = __copy_cv<_Tp, _Up>;
+};
+template <class _Tp>
+struct __xref<_Tp&>
+{
+    template <class _Up>
+    using __res_type = add_lvalue_reference_t<__copy_cv<_Tp, _Up>>;
+};
+template <class _Tp>
+struct __xref<_Tp&&>
+{
+    template <class _Up>
+    using __res_type = add_rvalue_reference_t<__copy_cv<_Tp, _Up>>;
+};
+
+//            COMMON-REF(A, B) is COND-RES(COPYCV(X, Y) &, COPYCV(​Y, X) &)
+//            if that type exists and is a reference type.
+
+template<class _Ap, class _Bp, class _Xp = remove_reference_t<_Ap>, class _Yp = remove_reference_t<_Bp>>
+struct __common_ref_
+{};
+
+template<class _Tp, class _Up>
+using __common_ref = typename __common_ref_<_Tp, _Up>::__type;
+
+template<class _Xp, class _Yp>
+requires (!is_reference_v<_Xp> && !is_reference_v<_Yp>)
+using __cv_cond_res = __cond_res<__copy_cv<_Xp, _Yp>&, __copy_cv<_Yp, _Xp>&>;
+
+template<class _Ap, class _Bp, class _Xp, class _Yp>
+requires requires { typename __cv_cond_res<_Xp, _Yp>; } && is_reference_v<__cv_cond_res<_Xp, _Yp>>
+struct __common_ref_<_Ap&, _Bp&, _Xp, _Yp>
+{
+    using __type = __cv_cond_res<_Xp, _Yp>;
+};
+
+//            Otherwise, let C be remove_­reference_­t<COMMON-REF(X&, Y&)>&&. If A and B are both
+//            rvalue reference types, C is well-formed, and ...
+template <class _Tp, class _Up>
+using __common_ref_C = remove_reference_t<__common_ref<_Tp&, _Up&>>&&;
+
+template<class _Ap, class _Bp, class _Xp, class _Yp>
+requires
+  requires { typename __common_ref_C<_Xp, _Yp>; } &&
+  is_convertible_v<_Ap, __common_ref_C<_Xp, _Yp>> &&
+  is_convertible_v<_Bp, __common_ref_C<_Xp, _Yp>>
+struct __common_ref_<_Ap&&, _Bp&&, _Xp, _Yp>
+{
+    using __type = __common_ref_C<_Xp, _Yp>;
+};
+
+//            Otherwise, let D be COMMON-REF(const X&, Y&).
+template <class _Tp, class _Up>
+using __common_ref_D = __common_ref<const _Tp&, _Up&>;
+
+
+template<class _Ap, class _Bp, class _Xp, class _Yp>
+requires requires { typename __common_ref_D<_Xp, _Yp>; } &&
+         is_convertible_v<_Ap, __common_ref_D<_Xp, _Yp>>
+struct __common_ref_<_Ap&&, _Bp&, _Xp, _Yp>
+{
+    using __type = __common_ref_D<_Xp, _Yp>;
+};
+
+//             Otherwise, if A is an lvalue reference and B is an rvalue reference,
+//             then COMMON-REF(A, B) is COMMON-REF(B, A)
+template<class _Ap, class _Bp, class _Xp, class _Yp>
+struct __common_ref_<_Ap&, _Bp&&, _Xp, _Yp> : __common_ref_<_Bp&&, _Ap&> {};
+
+// Note C: For the common_reference trait applied to a parameter pack [...]
+
+// bullet 1 - sizeof...(T) == 0
+template <class...>
+struct _LIBCPP_TEMPLATE_VIS common_reference {};
+
+template <class... _Types>
+using common_reference_t = typename common_reference<_Types...>::type;
+
+// bullet 2 - sizeof...(T) == 1
+template <class _Tp>
+struct _LIBCPP_TEMPLATE_VIS common_reference<_Tp>
+{
+    using type = _Tp;
+};
+
+// bullet 3 - sizeof...(T) == 2
+
+// sub-bullet 4 & 5 - [...] if common_type_t<T1, T2> is well-formed [...]
+//                  - Otherwise, there shall be no member type.
+template <class _Tp, class _Up>
+struct __common_reference4 : common_type<_Tp, _Up>
+{};
+
+// sub-bullet 3 - [...] if COND_RES(T1, T2) is well-formed [...]
+template <class _Tp, class _Up>
+requires requires { typename __cond_res<_Tp, _Up>; }
+struct __common_reference4<_Tp, _Up>
+{
+    using type = __cond_res<_Tp, _Up>;
+};
+
+// sub-bullet 2 - [...] if basic_common_reference<[...]>::type is well-formed [...]
+template <class, class, template <class> class, template <class> class>
+struct _LIBCPP_TEMPLATE_VIS basic_common_reference
+{};
+
+template <class _Tp, class _Up>
+using __basic_common_ref = typename basic_common_reference<
+    remove_cvref_t<_Tp>, remove_cvref_t<_Up>,
+    __xref<_Tp>::template __res_type, __xref<_Up>::template __res_type>::type;
+
+template <class _Tp, class _Up>
+struct __common_reference3 : __common_reference4<_Tp, _Up>
+{};
+
+template <class _Tp, class _Up>
+requires requires { typename __basic_common_ref<_Tp, _Up>; }
+struct __common_reference3<_Tp, _Up>
+{
+    using type = __basic_common_ref<_Tp, _Up>;
+};
+
+// sub-bullet 1 - If T1 and T2 are reference types and COMMON_REF(T1, T2) is well-formed [...]
+template <class _Tp, class _Up>
+struct __common_reference2 : __common_reference3<_Tp, _Up>
+{};
+
+template <class _Tp, class _Up>
+requires is_reference_v<_Tp> && is_reference_v<_Up> && requires { typename __common_ref<_Tp, _Up>; }
+struct __common_reference2<_Tp, _Up>
+{
+    using type = __common_ref<_Tp, _Up>;
+};
+
+template <class _Tp, class _Up>
+struct _LIBCPP_TEMPLATE_VIS common_reference<_Tp, _Up>
+    : __common_reference2<_Tp, _Up>
+{};
+
+// bullet 4 - sizeof...(T) > 2
+template <class _Tp, class _Up, class _Vp, class... _Rest>
+requires requires { typename common_reference_t<_Tp, _Up>; }
+struct _LIBCPP_TEMPLATE_VIS common_reference<_Tp, _Up, _Vp, _Rest...>
+    : common_reference<common_reference_t<_Tp, _Up>, _Vp, _Rest...>
+{};
+
+#endif // _LIBCPP_STD_VER > 17 && defined(__cpp_concepts) && __cpp_concepts >= 201811L
+
 // is_assignable
 
 template<typename, typename _Tp> struct __select_2nd { typedef _LIBCPP_NODEBUG_TYPE _Tp type; };
diff --git a/libcxx/test/std/utilities/meta/meta.trans/meta.trans.other/common_reference.compile.pass.cpp b/libcxx/test/std/utilities/meta/meta.trans/meta.trans.other/common_reference.compile.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/utilities/meta/meta.trans/meta.trans.other/common_reference.compile.pass.cpp
@@ -0,0 +1,196 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+
+// type_traits
+// common_reference
+
+#include <type_traits>
+
+using std::common_reference;
+using std::common_reference_t;
+using std::is_same_v;
+using std::void_t;
+
+template <class T>
+constexpr bool has_type = requires {
+  typename T::type;
+};
+
+// A slightly simplified variation of std::tuple
+template <class...>
+struct Tuple {};
+
+template <class, class, class>
+struct Tuple_helper {};
+template <class... Ts, class... Us>
+struct Tuple_helper<void_t<common_reference_t<Ts, Us>...>, Tuple<Ts...>,
+                    Tuple<Us...> > {
+  using type = Tuple<common_reference_t<Ts, Us>...>;
+};
+
+namespace std {
+template <class... Ts, class... Us, template <class> class TQual,
+          template <class> class UQual>
+struct basic_common_reference< ::Tuple<Ts...>, ::Tuple<Us...>, TQual, UQual>
+    : ::Tuple_helper<void, Tuple<TQual<Ts>...>, Tuple<UQual<Us>...> > {};
+} // namespace std
+
+struct X2 {};
+struct Y2 {};
+struct Z2 {};
+
+namespace std {
+template <>
+struct common_type<X2, Y2> {
+  using type = Z2;
+};
+template <>
+struct common_type<Y2, X2> {
+  using type = Z2;
+};
+} // namespace std
+
+// (6.1)
+//  -- If sizeof...(T) is zero, there shall be no member type.
+static_assert(!has_type<common_reference<> >);
+
+// (6.2)
+//  -- Otherwise, if sizeof...(T) is one, let T0 denote the sole type in the
+//     pack T. The member typedef type shall denote the same type as T0.
+static_assert(is_same_v<common_reference_t<void>, void>);
+static_assert(is_same_v<common_reference_t<int>, int>);
+static_assert(is_same_v<common_reference_t<int&>, int&>);
+static_assert(is_same_v<common_reference_t<int&&>, int&&>);
+static_assert(is_same_v<common_reference_t<int const>, int const>);
+static_assert(is_same_v<common_reference_t<int const&>, int const&>);
+static_assert(is_same_v<common_reference_t<int const&&>, int const&&>);
+static_assert(is_same_v<common_reference_t<int volatile[]>, int volatile[]>);
+static_assert(
+    is_same_v<common_reference_t<int volatile (&)[]>, int volatile (&)[]>);
+static_assert(
+    is_same_v<common_reference_t<int volatile(&&)[]>, int volatile(&&)[]>);
+static_assert(is_same_v<common_reference_t<void (&)()>, void (&)()>);
+static_assert(is_same_v<common_reference_t<void(&&)()>, void(&&)()>);
+
+// (6.3)
+//  -- Otherwise, if sizeof...(T) is two, let T1 and T2 denote the two types in
+//     the pack T. Then
+// (6.3.1)
+//    -- If T1 and T2 are reference types and COMMON_REF(T1, T2) is well-formed,
+//       then the member typedef type denotes that type.
+struct B {};
+struct D : B {};
+static_assert(is_same_v<common_reference_t<B&, D&>, B&>);
+static_assert(is_same_v<common_reference_t<B const&, D&>, B const&>);
+static_assert(is_same_v<common_reference_t<B&, D const&>, B const&>);
+static_assert(is_same_v<common_reference_t<B&, D const&, D&>, B const&>);
+static_assert(is_same_v<common_reference_t<B&, D&, B&, D&>, B&>);
+
+static_assert(is_same_v<common_reference_t<B&&, D&&>, B&&>);
+static_assert(is_same_v<common_reference_t<B const&&, D&&>, B const&&>);
+static_assert(is_same_v<common_reference_t<B&&, D const&&>, B const&&>);
+static_assert(is_same_v<common_reference_t<B&, D&&>, B const&>);
+static_assert(is_same_v<common_reference_t<B&, D const&&>, B const&>);
+static_assert(is_same_v<common_reference_t<B const&, D&&>, B const&>);
+
+static_assert(is_same_v<common_reference_t<B&&, D&>, B const&>);
+static_assert(is_same_v<common_reference_t<B&&, D const&>, B const&>);
+static_assert(is_same_v<common_reference_t<B const&&, D&>, B const&>);
+
+static_assert(
+    is_same_v<common_reference_t<int const volatile&&, int volatile&&>,
+              int const volatile&&>);
+
+static_assert(is_same_v<common_reference_t<int const&, int volatile&>,
+                        int const volatile&>);
+
+static_assert(
+    is_same_v<common_reference_t<int (&)[10], int(&&)[10]>, int const (&)[10]>);
+
+static_assert(
+    is_same_v<common_reference_t<int const (&)[10], int volatile (&)[10]>,
+              int const volatile (&)[10]>);
+
+// (6.3.2)
+//    -- Otherwise, if basic_common_reference<remove_cvref_t<T1>,
+//       remove_cvref_t<T2>, XREF(T1), XREF(T2)>::type is well-formed, then the
+//       member typedef type denotes that type.
+static_assert(is_same_v<common_reference_t<const Tuple<int, short>&,
+                                           Tuple<int&, short volatile&> >,
+                        Tuple<const int&, const volatile short&> >);
+
+static_assert(is_same_v<common_reference_t<volatile Tuple<int, short>&,
+                                           const Tuple<int, short>&>,
+                        const volatile Tuple<int, short>&>);
+
+// (6.3.3)
+//    -- Otherwise, if COND_RES(T1, T2) is well-formed, then the member typedef
+//       type denotes that type.
+static_assert(is_same_v<common_reference_t<void, void>, void>);
+static_assert(is_same_v<common_reference_t<int, short>, int>);
+static_assert(is_same_v<common_reference_t<int, short&>, int>);
+static_assert(is_same_v<common_reference_t<int&, short&>, int>);
+static_assert(is_same_v<common_reference_t<int&, short>, int>);
+
+// tricky volatile reference case
+static_assert(is_same_v<common_reference_t<int&&, int volatile&>, int>);
+static_assert(is_same_v<common_reference_t<int volatile&, int&&>, int>);
+
+static_assert(is_same_v<common_reference_t<int (&)[10], int (&)[11]>, int*>);
+
+// https://github.com/ericniebler/stl2/issues/338
+struct MyIntRef {
+  MyIntRef(int&);
+};
+static_assert(is_same_v<common_reference_t<int&, MyIntRef>, MyIntRef>);
+
+// (6.3.4)
+//    -- Otherwise, if common_type_t<T1, T2> is well-formed, then the member
+//       typedef type denotes that type.
+struct moveonly {
+  moveonly() = default;
+  moveonly(moveonly&&) = default;
+  moveonly& operator=(moveonly&&) = default;
+};
+struct moveonly2 : moveonly {};
+
+static_assert(
+    is_same_v<common_reference_t<moveonly const&, moveonly>, moveonly>);
+static_assert(
+    is_same_v<common_reference_t<moveonly2 const&, moveonly>, moveonly>);
+static_assert(
+    is_same_v<common_reference_t<moveonly const&, moveonly2>, moveonly>);
+
+static_assert(is_same_v<common_reference_t<X2&, Y2 const&>, Z2>);
+
+// (6.3.5)
+//    -- Otherwise, there shall be no member type.
+static_assert(!has_type<common_reference<volatile Tuple<short>&,
+                                         const Tuple<int, short>&> >);
+
+// (6.4)
+//  -- Otherwise, if sizeof...(T) is greater than two, let T1, T2, and Rest,
+//     respectively, denote the first, second, and (pack of) remaining types
+//     comprising T. Let C be the type common_reference_t<T1, T2>. Then:
+// (6.4.1)
+//    -- If there is such a type C, the member typedef type shall denote the
+//       same type, if any, as common_reference_t<C, Rest...>.
+static_assert(is_same_v<common_reference_t<int, int, int>, int>);
+static_assert(is_same_v<common_reference_t<int&&, int const&, int volatile&>,
+                        int const volatile&>);
+static_assert(is_same_v<common_reference_t<int&&, int const&, float&>, float>);
+
+// (6.4.2)
+//    -- Otherwise, there shall be no member type.
+static_assert(!has_type<common_reference<int, short, int, char*> >);
+
+int main(int, char**) { return 0; }