diff --git a/libcxx/include/iterator b/libcxx/include/iterator
--- a/libcxx/include/iterator
+++ b/libcxx/include/iterator
@@ -18,7 +18,12 @@
 namespace std
 {
 template<class> struct incrementable_traits;       // since C++20
+template<class T>
+  using iter_difference_t = see below;             // since C++20
+
 template<class> struct indirectly_readable_traits; // since C++20
+template<class T>
+  using iter_value_t = see below;                  // since C++20
 
 template<class Iterator>
 struct iterator_traits
@@ -437,6 +442,9 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
+template <class _Iter>
+struct _LIBCPP_TEMPLATE_VIS iterator_traits;
+
 #if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_CONCEPTS)
 // [incrementable.traits]
 template<class> struct incrementable_traits {};
@@ -470,7 +478,27 @@
   using difference_type = make_signed_t<decltype(declval<_Tp>() - declval<_Tp>())>;
 };
 
-// TODO(cjdb): add iter_difference_t once iterator_traits is cleaned up.
+// Let `R[I]` be `remove_­cvref_­t<I>`. The type `iter_­difference_­t<I>` denotes
+template<class>
+struct __extract_iter_difference_t;
+
+template<class _Ip>
+using iter_difference_t = typename __extract_iter_difference_t<remove_cvref_t<_Ip>>::type;
+
+// `incrementable_­traits<R[I]>::difference_­type` if `iterator_­traits<R[I]>` names a specialization
+// generated from the primary template, and
+template<typename _Ip>
+requires __is_primary_template<iterator_traits<_Ip>>::value &&
+         (__has_member_difference_type<_Ip> || __has_integral_minus<_Ip>)
+struct __extract_iter_difference_t<_Ip> {
+  using type = typename incrementable_traits<_Ip>::difference_type;
+};
+
+// `iterator_­traits<R[I]>::difference_­type` otherwise.
+template<typename _Ip>
+struct __extract_iter_difference_t {
+  using type = typename iterator_traits<_Ip>::difference_type;
+};
 
 // [readable.traits]
 template<class> struct indirectly_readable_traits {};
@@ -518,7 +546,27 @@
 struct indirectly_readable_traits<_Tp>
   : __cond_value_type<typename _Tp::value_type> {};
 
-// TODO(cjdb): add iter_value_t once iterator_traits is cleaned up.
+// Let `R[I]` be `remove_­cvref_­t<I>`. The type `iter_­value_­t<I>` denotes
+template<class>
+struct __extract_iter_value_t;
+
+template<class _Ip>
+using iter_value_t = typename __extract_iter_value_t<remove_cvref_t<_Ip>>::type;
+
+// indirectly_­readable_­traits<R[I]>::value_­type if `iterator_­traits<R[I]>` names a specialization
+// generated from the primary template, and
+template<class _Ip>
+requires __is_primary_template<iterator_traits<_Ip>>::value &&
+         __has_member_value_type<indirectly_readable_traits<_Ip>>
+struct __extract_iter_value_t<_Ip> {
+  using type = typename indirectly_readable_traits<_Ip>::value_type;
+};
+
+// iterator_­traits<R[I]>::value_­type otherwise.
+template<class _Ip>
+struct __extract_iter_value_t {
+  using type = typename iterator_traits<_Ip>::value_type;
+};
 
 template<class _Tp>
 using __with_reference = _Tp&;
@@ -537,9 +585,6 @@
 using iter_reference_t = decltype(*declval<_Tp&>());
 #endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_CONCEPTS)
 
-template <class _Iter>
-struct _LIBCPP_TEMPLATE_VIS iterator_traits;
-
 struct _LIBCPP_TEMPLATE_VIS input_iterator_tag {};
 struct _LIBCPP_TEMPLATE_VIS output_iterator_tag {};
 struct _LIBCPP_TEMPLATE_VIS forward_iterator_tag       : public input_iterator_tag {};
diff --git a/libcxx/test/std/iterators/iterator.requirements/iterator.assoc.types/incrementable.traits/iter_difference_t.fail.cpp b/libcxx/test/std/iterators/iterator.requirements/iterator.assoc.types/incrementable.traits/iter_difference_t.fail.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/iterators/iterator.requirements/iterator.assoc.types/incrementable.traits/iter_difference_t.fail.cpp
@@ -0,0 +1,34 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// template<class T>
+// using iter_difference_t;
+
+#include <iterator>
+
+using fails1 = std::iter_difference_t<void>;
+// expected-error@iterator:* {{no type named 'difference_type' in 'std::iterator_traits<void>'}}
+
+using fails2 = std::iter_difference_t<double>;
+// expected-error@iterator:* {{no type named 'difference_type' in 'std::iterator_traits<double>'}}
+
+struct S {};
+using fails3 = std::iter_difference_t<S>;
+// expected-error@iterator:* {{no type named 'difference_type' in 'std::iterator_traits<S>'}}
+
+struct void_subtraction {
+  friend void operator-(void_subtraction, void_subtraction);
+};
+using fails4 = std::iter_difference_t<void_subtraction>;
+// expected-error@iterator:* {{no type named 'difference_type' in 'std::iterator_traits<void_subtraction>'}}
+
+int main(int, char**) { return 0; }
diff --git a/libcxx/test/std/iterators/iterator.requirements/iterator.assoc.types/incrementable.traits/iter_difference_t.pass.cpp b/libcxx/test/std/iterators/iterator.requirements/iterator.assoc.types/incrementable.traits/iter_difference_t.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/iterators/iterator.requirements/iterator.assoc.types/incrementable.traits/iter_difference_t.pass.cpp
@@ -0,0 +1,60 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// template<class T>
+// using iter_difference_t;
+
+#include <iterator>
+
+#include <concepts>
+#include <vector>
+
+template <class T, class Expected>
+[[nodiscard]] constexpr bool check_iter_difference_t() {
+  constexpr bool result = std::same_as<std::iter_difference_t<T>, Expected>;
+  static_assert(std::same_as<std::iter_difference_t<T const>, Expected> ==
+                result);
+  static_assert(std::same_as<std::iter_difference_t<T volatile>, Expected> ==
+                result);
+  static_assert(
+      std::same_as<std::iter_difference_t<T const volatile>, Expected> ==
+      result);
+  static_assert(std::same_as<std::iter_difference_t<T const&>, Expected> ==
+                result);
+  static_assert(std::same_as<std::iter_difference_t<T volatile&>, Expected> ==
+                result);
+  static_assert(
+      std::same_as<std::iter_difference_t<T const volatile&>, Expected> ==
+      result);
+  static_assert(std::same_as<std::iter_difference_t<T const&&>, Expected> ==
+                result);
+  static_assert(std::same_as<std::iter_difference_t<T volatile&&>, Expected> ==
+                result);
+  static_assert(
+      std::same_as<std::iter_difference_t<T const volatile&&>, Expected> ==
+      result);
+
+  return result;
+}
+
+static_assert(check_iter_difference_t<int, int>());
+static_assert(check_iter_difference_t<int*, std::ptrdiff_t>());
+static_assert(
+    check_iter_difference_t<std::vector<int>::iterator,
+                            std::vector<int>::iterator::difference_type>());
+
+struct int_subtraction {
+  friend int operator-(int_subtraction, int_subtraction) noexcept;
+};
+static_assert(check_iter_difference_t<int_subtraction, int>());
+
+int main(int, char**) { return 0; }
diff --git a/libcxx/test/std/iterators/iterator.requirements/iterator.assoc.types/readable.traits/iter_value_t.fail.cpp b/libcxx/test/std/iterators/iterator.requirements/iterator.assoc.types/readable.traits/iter_value_t.fail.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/iterators/iterator.requirements/iterator.assoc.types/readable.traits/iter_value_t.fail.cpp
@@ -0,0 +1,35 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// template<class T>
+// using iter_value_t;
+
+#include <iterator>
+
+using fail1 = std::iter_value_t<void>;
+// expected-error@iterator:* {{no type named 'value_type' in 'std::iterator_traits<void>'}}
+
+using fail2 = std::iter_value_t<int>;
+// expected-error@iterator:* {{no type named 'value_type' in 'std::iterator_traits<int>'}}
+
+struct S {};
+using fail3 = std::iter_value_t<S>;
+// expected-error@iterator:* {{no type named 'value_type' in 'std::iterator_traits<S>'}}
+
+struct different_value_element {
+  using value_type = int;
+  using element_type = long;
+};
+using fail4 = std::iter_value_t<different_value_element>;
+// expected-error@iterator:* {{no type named 'value_type' in 'std::iterator_traits<different_value_element>'}}
+
+int main(int, char**) { return 0; }
diff --git a/libcxx/test/std/iterators/iterator.requirements/iterator.assoc.types/readable.traits/iter_value_t.pass.cpp b/libcxx/test/std/iterators/iterator.requirements/iterator.assoc.types/readable.traits/iter_value_t.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/iterators/iterator.requirements/iterator.assoc.types/readable.traits/iter_value_t.pass.cpp
@@ -0,0 +1,58 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// template<class T>
+// using iter_value_t;
+
+#include <iterator>
+
+#include <concepts>
+#include <memory>
+#include <vector>
+
+template <class T, class Expected>
+[[nodiscard]] constexpr bool check_iter_value_t() {
+  constexpr bool result = std::same_as<std::iter_value_t<T>, Expected>;
+  static_assert(std::same_as<std::iter_value_t<T const>, Expected> == result);
+  static_assert(std::same_as<std::iter_value_t<T volatile>, Expected> ==
+                result);
+  static_assert(std::same_as<std::iter_value_t<T const volatile>, Expected> ==
+                result);
+  static_assert(std::same_as<std::iter_value_t<T const&>, Expected> == result);
+  static_assert(std::same_as<std::iter_value_t<T volatile&>, Expected> ==
+                result);
+  static_assert(std::same_as<std::iter_value_t<T const volatile&>, Expected> ==
+                result);
+  static_assert(std::same_as<std::iter_value_t<T const&&>, Expected> == result);
+  static_assert(std::same_as<std::iter_value_t<T volatile&&>, Expected> ==
+                result);
+  static_assert(std::same_as<std::iter_value_t<T const volatile&&>, Expected> ==
+                result);
+
+  return result;
+}
+
+static_assert(check_iter_value_t<int*, int>());
+static_assert(check_iter_value_t<int[], int>());
+static_assert(check_iter_value_t<int[10], int>());
+static_assert(check_iter_value_t<std::vector<int>::iterator,
+                                 std::vector<int>::iterator::value_type>());
+static_assert(check_iter_value_t<std::shared_ptr<int>,
+                                 std::shared_ptr<int>::element_type>());
+
+struct both_members {
+  using value_type = double;
+  using element_type = double;
+};
+static_assert(check_iter_value_t<both_members, double>());
+
+int main(int, char**) { return 0; }