Index: include/algorithm
===================================================================
--- include/algorithm
+++ include/algorithm
@@ -631,6 +631,19 @@
     bool
     prev_permutation(BidirectionalIterator first, BidirectionalIterator last, Compare comp);
 
+template<class ForwardIterator>
+    ForwardIterator shift_left(ForwardIterator first, ForwardIterator last,
+                                         typename iterator_traits<ForwardIterator>::difference_type n);
+template<class ExecutionPolicy, class ForwardIterator>
+    ForwardIterator shift_left(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last,
+                               typename iterator_traits<ForwardIterator>::difference_type n);
+template<class ForwardIterator>
+    ForwardIterator shift_right(ForwardIterator first, ForwardIterator last,
+                                typename iterator_traits<ForwardIterator>::difference_type n);
+template<class ExecutionPolicy, class ForwardIterator>
+    ForwardIterator shift_right(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last,
+                                typename iterator_traits<ForwardIterator>::difference_type n);
+
 }  // std
 
 */
@@ -5781,6 +5794,72 @@
                                   __less<typename iterator_traits<_BidirectionalIterator>::value_type>());
 }
 
+#if _LIBCPP_VERSION > 17
+
+template<class _It>
+_LIBCPP_CONSTEXPR_AFTER_CXX14 _It
+shift_left(_It __first, _It __last, typename iterator_traits<_It>::difference_type __n)
+{
+    auto __size = _VSTD::distance(__first, __last);
+    if (__n <= 0 || __size <= 0 || __n >= __size) return __first;
+
+    for (unsigned __i = 0; __i < __n; ++__i, ++__first) {};
+
+    return __first;
+}
+
+template<class _Ep, class _It>
+_LIBCPP_CONSTEXPR_AFTER_CXX14 _It
+shift_left(_Ep&&, _It __first, _It __last, typename iterator_traits<_It>::difference_type __n)
+{ return shift_left(__first, __last, __n); }
+
+template<class _It, class _Ft>
+_LIBCPP_CONSTEXPR_AFTER_CXX14 typename enable_if<
+    !is_same<forward_iterator_tag, _Ft>::value,
+    _It
+>::type
+__shift_right_impl(_It __first, _It __last, typename iterator_traits<_It>::difference_type __n, _Ft)
+{
+    auto __size = _VSTD::distance(__first, __last);
+    if (__n <= 0 || __size <= 0 || __n >= __size) return __first;
+
+    auto __mid = __last;
+    for (unsigned __i = 0; __i < __n; ++__i, --__mid) {};
+
+    return move_backward(__first, __mid, __last);
+}
+
+template<class _It, class _Ft>
+_LIBCPP_CONSTEXPR_AFTER_CXX14 typename enable_if<
+    is_same<forward_iterator_tag, _Ft>::value,
+    _It
+>::type
+__shift_right_impl(_It __first, _It __last, typename iterator_traits<_It>::difference_type __n, _Ft)
+{
+    auto __size = _VSTD::distance(__first, __last);
+    if (__n <= 0 || __size <= 0 || __n >= __size) return __first;
+
+    auto __mid = __first;
+    for (unsigned __i = 0; __i < (__size - __n); ++__i, ++__mid) {};
+    __rotate_forward(__first, __mid, __last);
+
+    for (unsigned __i = 0; __i < __n; ++__i, ++__first) {};
+    return __first;
+}
+
+template<class _It>
+_LIBCPP_CONSTEXPR_AFTER_CXX14 _It
+shift_right(_It __first, _It __last, typename iterator_traits<_It>::difference_type __n)
+{ return __shift_right_impl(__first, __last, __n,
+                            typename std::iterator_traits<_It>::iterator_category()); }
+
+template<class _Ep, class _It>
+_LIBCPP_CONSTEXPR_AFTER_CXX14 _It
+shift_right(_Ep&&, _It __first, _It __last, typename iterator_traits<_It>::difference_type __n)
+{ return shift_right(__first, __last, __n); }
+
+#endif // _LIBCPP_VERSION > 17
+
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
Index: test/std/algorithms/alg.shift/shift_exec_policy.pass.cpp
===================================================================
--- /dev/null
+++ test/std/algorithms/alg.shift/shift_exec_policy.pass.cpp
@@ -0,0 +1,67 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// <algorithm>
+
+//	  template<class ForwardIterator>
+//	  ForwardIterator shift_left(ForwardIterator first, ForwardIterator last,
+//								 typename iterator_traits<ForwardIterator>::difference_type n);
+//	  template<class ExecutionPolicy, class ForwardIterator>
+//	  ForwardIterator shift_left(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last,
+//								 typename iterator_traits<ForwardIterator>::difference_type n);
+//	  template<class ForwardIterator>
+//	  ForwardIterator shift_right(ForwardIterator first, ForwardIterator last,
+//								  typename iterator_traits<ForwardIterator>::difference_type n);
+//	  template<class ExecutionPolicy, class ForwardIterator>
+//	  ForwardIterator shift_right(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last,
+//								  typename iterator_traits<ForwardIterator>::difference_type n);
+
+#include <algorithm>
+#include <vector>
+#include <numeric>
+
+template<class T, class It>
+void test(T container, It begin, It end)
+{
+	auto left_check = container[20];
+	auto right_check = container[0];
+
+	auto shifted_container = shift_left(begin, end, 20);
+	assert(left_check == shifted_container[0]);
+	shifted_container = shift_right(begin, end, 20);
+	assert(right_check == shifted_container[0]);
+}
+
+struct E
+{
+	unsigned x;
+	bool operator==(E rhs) { return x == rhs.x; }
+};
+
+int main(int, char**)
+{
+	std::vector<int> vec(100);
+	std::iota(vec.begin(), vec.end(), 0);
+
+	std::vector<E> evec;
+	for (unsigned i = 0; i < 100; ++i) evec.push_back(E { i });
+
+	int arr[100];
+	for (unsigned i = 0; i < 100; ++i) arr[i] = i;
+
+	test(vec, vec.begin(), vec.end());
+	test(evec, evec.begin(), evec.end());
+	test(arr, arr, arr + 100);
+
+	// Execution policy overloads:
+	// The execution policies have no effect on the shift function.
+	shift_left(/*std::execution::sequenced_policy*/ 0, vec.begin(), vec.end(), 0);
+	shift_right(/*std::execution::parallel_policy*/ 1, vec.begin(), vec.end(), 0);
+
+	return 0;
+}
Index: test/std/algorithms/alg.shift/shift_left.pass.cpp
===================================================================
--- /dev/null
+++ test/std/algorithms/alg.shift/shift_left.pass.cpp
@@ -0,0 +1,137 @@
+//===----------------------------------------------------------------------===//
+//
+//					   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++98, c++03, c++11, c++14, c++17
+
+// <algorithm>
+
+// template<class ForwardIterator>
+//	   constexpr ForwardIterator
+//	   shift_left(ForwardIterator first, ForwardIterator last,
+//				  typename iterator_traits<ForwardIterator>::difference_type n); // C++20
+//
+// Effects: If n <= 0 or n >= last - first, does nothing. 
+//			Otherwise, moves the element from position first + n + i into position
+//			first + i for each non-negative integer i < (last - first) - n.
+//			Does so in order starting from i = 0 and proceeding to i = (last - first) - n - 1.
+// 
+// Returns: first + (last - first - n) if n is positive and n < last - first, 
+//		   otherwise first if n is positive, otherwise last.
+
+
+#include <algorithm>
+#include <cassert>
+#include <iterator>
+#include <numeric>
+#include <array>
+
+#include "test_macros.h"
+#include "test_iterators.h"
+
+struct MInt 
+{
+	MInt (int v) : v_{v} {}
+	MInt (	   ) : v_{0} {}
+	
+	MInt (const MInt  &rhs) : v_{rhs.v_} {}
+	MInt (		MInt &&rhs) : v_{rhs.v_} { rhs.v_ = -1;}
+	
+	MInt& operator=(const MInt	&rhs) { v_ = rhs.v_;			  return *this; }
+	MInt& operator=(	  MInt &&rhs) { v_ = rhs.v_; rhs.v_ = -1; return *this; }
+
+	int v_;
+};
+
+bool operator==(const MInt &rhs, const MInt &lhs)
+{ return lhs.v_ == rhs.v_ && lhs.v_ != -1; } // we shouldn't be comparing moved-from objects
+
+template <class Iter>
+void test()
+{
+	using T = typename std::iterator_traits<Iter>::value_type;
+	
+	// n < 0
+	{
+		T input[]		   = {0, 1, 2};
+		const T expected[] = {0, 1, 2};
+		Iter b = Iter(std::begin(input));
+		Iter e = Iter(std::end(input));
+		Iter it = std::shift_left(b, e, -1);
+		assert(std::equal(std::begin(expected), std::end(expected), b));
+		assert(it == b);
+	}
+
+	// n == 0
+	{
+		T input[]		   = {0, 1, 2};
+		const T expected[] = {0, 1, 2};
+		Iter b = Iter(std::begin(input));
+		Iter e = Iter(std::end(input));
+		Iter it = std::shift_left(b, e, 0);
+		assert(std::equal(std::begin(expected), std::end(expected), b));
+		assert(it == b);
+	}
+
+	// n > 0 && n < len
+	for (size_t n = 1; n < 10; ++n)
+	{
+		T input[] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
+		
+		std::array<T, 10> expected;
+		std::iota(expected.begin(), expected.end(), n);
+
+		Iter b = Iter(std::begin(input));
+		Iter e = Iter(std::end(input));
+		Iter it = std::shift_left(b, e, n);
+
+		for (unsigned x = 0; x < 10 - n; ++x)
+			assert(*it++ == expected[x]);
+
+	//	The complication here (the "min") is because things are different when the
+	//	shift count is more than half the size of the sequence.
+	//	I don't think this is necessary?
+	// assert(std::all_of(std::next(b, std::size(input) - std::min(n, std::size(input) - n)), e, hasBeenMoved<T>));
+	}
+
+	// n == len
+	{
+		T input[]		   = {0, 1, 2};
+		const T expected[] = {0, 1, 2};
+		Iter b = Iter(std::begin(input));
+		Iter e = Iter(std::end(input));
+		Iter it = std::shift_left(b, e, std::size(input));
+		assert(std::equal(std::begin(expected), std::end(expected), b));
+		assert(it == b);
+	}
+
+	// n > len
+	{
+		T input[]		   = {0, 1, 2};
+		const T expected[] = {0, 1, 2};
+		Iter b = Iter(std::begin(input));
+		Iter e = Iter(std::end(input));
+		Iter it = std::shift_left(b, e, std::size(input) + 1);
+		assert(std::equal(std::begin(expected), std::end(expected), b));
+		assert(it == b);
+	}
+}
+
+int main(int, char**)
+{
+	test<forward_iterator<int*>>();
+	test<bidirectional_iterator<int*>>();
+	test<random_access_iterator<int*>>();
+	test<int*>();
+
+	test<forward_iterator<MInt*>>();
+	test<bidirectional_iterator<MInt*>>();
+	test<random_access_iterator<MInt*>>();
+	test<MInt*>();
+	
+	return 0;
+}
Index: test/std/algorithms/alg.shift/shift_right.pass.cpp
===================================================================
--- /dev/null
+++ test/std/algorithms/alg.shift/shift_right.pass.cpp
@@ -0,0 +1,137 @@
+//===----------------------------------------------------------------------===//
+//
+//					   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++98, c++03, c++11, c++14, c++17
+
+// <algorithm>
+
+// template<class ForwardIterator>
+//	   constexpr ForwardIterator
+//	   shift_right(ForwardIterator first, ForwardIterator last,
+//				  typename iterator_traits<ForwardIterator>::difference_type n); // C++20
+//
+// Effects: If n <= 0 or n >= last - first, does nothing. 
+//			Otherwise, moves the element from position first + i into position
+//			first + n + i for each non-negative integer i < (last - first) - n.
+//			If ForwardIterator satisfies the Cpp17BidirectionalIterator requirements,
+//			does so in order starting from i = (last - first) - n - 1 and proceeding to i = 0.
+// 
+// Returns: first + n if n is positive and n < last - first, 
+//			otherwise last if n is positive, otherwise first.
+
+#include <algorithm>
+#include <cassert>
+#include <iterator>
+#include <numeric>
+#include <array>
+
+#include "test_macros.h"
+#include "test_iterators.h"
+
+struct MInt 
+{
+	MInt (int v) : v_{v} {}
+	MInt (	   ) : v_{0} {}
+	
+	MInt (const MInt  &rhs) : v_{rhs.v_} {}
+	MInt (		MInt &&rhs) : v_{rhs.v_} { rhs.v_ = -1;}
+	
+	MInt& operator=(const MInt	&rhs) { v_ = rhs.v_;			  return *this; }
+	MInt& operator=(	  MInt &&rhs) { v_ = rhs.v_; rhs.v_ = -1; return *this; }
+
+	int v_;
+};
+
+bool operator==(const MInt &rhs, const MInt &lhs)
+{ return lhs.v_ == rhs.v_ && lhs.v_ != -1; } // we shouldn't be comparing moved-from objects
+
+template <class Iter>
+void test()
+{
+	using T = typename std::iterator_traits<Iter>::value_type;
+	
+	// n < 0
+	{
+		T input[]		   = {0, 1, 2};
+		const T expected[] = {0, 1, 2};
+		Iter b = Iter(std::begin(input));
+		Iter e = Iter(std::end(input));
+		Iter it = std::shift_left(b, e, -1);
+		assert(std::equal(std::begin(expected), std::end(expected), b));
+		assert(it == b);
+	}
+
+	// n == 0
+	{
+		T input[]		   = {0, 1, 2};
+		const T expected[] = {0, 1, 2};
+		Iter b = Iter(std::begin(input));
+		Iter e = Iter(std::end(input));
+		Iter it = std::shift_left(b, e, 0);
+		assert(std::equal(std::begin(expected), std::end(expected), b));
+		assert(it == b);
+	}
+
+	// n > 0 && n < len
+	for (size_t n = 1; n < 10; ++n)
+	{
+		T input[] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
+		
+		std::array<T, 10> expected;
+		std::iota(expected.begin(), expected.end(), 0);
+
+		Iter b = Iter(std::begin(input));
+		Iter e = Iter(std::end(input));
+		Iter it = std::shift_right(b, e, n);
+
+		for (unsigned i = 0; i < 10 - n; ++i)
+			assert(*it++ == expected[i]);
+
+	//	The complication here (the "min") is because things are different when the
+	//	shift count is more than half the size of the sequence.
+	//	I don't think this is necessary?
+	// assert(std::all_of(std::next(b, std::size(input) - std::min(n, std::size(input) - n)), e, hasBeenMoved<T>));
+	}
+
+	// n == len
+	{
+		T input[]		   = {0, 1, 2};
+		const T expected[] = {0, 1, 2};
+		Iter b = Iter(std::begin(input));
+		Iter e = Iter(std::end(input));
+		Iter it = std::shift_left(b, e, std::size(input));
+		assert(std::equal(std::begin(expected), std::end(expected), b));
+		assert(it == b);
+	}
+
+	// n > len
+	{
+		T input[]		   = {0, 1, 2};
+		const T expected[] = {0, 1, 2};
+		Iter b = Iter(std::begin(input));
+		Iter e = Iter(std::end(input));
+		Iter it = std::shift_left(b, e, std::size(input) + 1);
+		assert(std::equal(std::begin(expected), std::end(expected), b));
+		assert(it == b);
+	}
+}
+
+int main(int, char**)
+{
+	test<forward_iterator<int*>>();
+	test<bidirectional_iterator<int*>>();
+	test<random_access_iterator<int*>>();
+	test<int*>();
+
+	test<forward_iterator<MInt*>>();
+	test<bidirectional_iterator<MInt*>>();
+	test<random_access_iterator<MInt*>>();
+	test<MInt*>();
+	
+	return 0;
+}