diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 6b3fc9485ec1a..e615702f7bbb8 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -1249,6 +1249,7 @@ if(LLVM_LIBC_FULL_BUILD)
 
     # wchar.h entrypoints
     libc.src.wchar.mbrtowc
+    libc.src.wchar.mbsrtowcs
     libc.src.wchar.mbtowc
     libc.src.wchar.wcrtomb
     libc.src.wchar.wctomb
diff --git a/libc/include/wchar.yaml b/libc/include/wchar.yaml
index 397296894829d..576cf09b86696 100644
--- a/libc/include/wchar.yaml
+++ b/libc/include/wchar.yaml
@@ -38,6 +38,15 @@ functions:
       - type: const char *__restrict
       - type: size_t
       - type: mbstate_t *__restrict
+  - name: mbsrtowcs
+    standards:
+      - stdc
+    return_type: size_t
+    arguments:
+      - type: wchar_t *__restrict
+      - type: const char **__restrict
+      - type: size_t
+      - type: mbstate_t *__restrict
   - name: mbtowc
     standards:
       - stdc
diff --git a/libc/src/__support/wchar/CMakeLists.txt b/libc/src/__support/wchar/CMakeLists.txt
index 86a47319f278a..c06b1023180ad 100644
--- a/libc/src/__support/wchar/CMakeLists.txt
+++ b/libc/src/__support/wchar/CMakeLists.txt
@@ -53,3 +53,19 @@ add_object_library(
   .character_converter
   .mbstate
 )
+
+add_object_library(
+  mbsrtowcs
+  HDRS
+    mbsrtowcs.h
+  SRCS
+    mbsrtowcs.cpp
+  DEPENDS
+  libc.hdr.types.wchar_t
+  libc.hdr.types.size_t
+  libc.src.__support.common
+  libc.src.__support.error_or
+  libc.src.__support.macros.config
+  .mbstate
+  .mbrtowc
+)
diff --git a/libc/src/__support/wchar/character_converter.cpp b/libc/src/__support/wchar/character_converter.cpp
index c54a1b751f402..af48e7d332667 100644
--- a/libc/src/__support/wchar/character_converter.cpp
+++ b/libc/src/__support/wchar/character_converter.cpp
@@ -27,7 +27,6 @@ constexpr uint32_t MASK_ENCODED_BITS =
     mask_trailing_ones<uint32_t, ENCODED_BITS_PER_UTF8>();
 // Maximum value for utf-32 for a utf-8 sequence of a given length
 constexpr char32_t MAX_VALUE_PER_UTF8_LEN[] = {0x7f, 0x7ff, 0xffff, 0x10ffff};
-constexpr int MAX_UTF8_LENGTH = 4;
 
 CharacterConverter::CharacterConverter(mbstate *mbstate) { state = mbstate; }
 
diff --git a/libc/src/__support/wchar/character_converter.h b/libc/src/__support/wchar/character_converter.h
index d9a63fdc0522c..f032005a79dd5 100644
--- a/libc/src/__support/wchar/character_converter.h
+++ b/libc/src/__support/wchar/character_converter.h
@@ -18,6 +18,8 @@
 namespace LIBC_NAMESPACE_DECL {
 namespace internal {
 
+constexpr int MAX_UTF8_LENGTH = 4;
+
 class CharacterConverter {
 private:
   mbstate *state;
diff --git a/libc/src/__support/wchar/mbrtowc.cpp b/libc/src/__support/wchar/mbrtowc.cpp
index 3b8f7666026c3..ae61999bdb1dc 100644
--- a/libc/src/__support/wchar/mbrtowc.cpp
+++ b/libc/src/__support/wchar/mbrtowc.cpp
@@ -36,7 +36,7 @@ ErrorOr<size_t> mbrtowc(wchar_t *__restrict pwc, const char *__restrict s,
       return Error(EILSEQ);
   }
   auto wc = char_conv.pop_utf32();
-  if (wc.has_value()) {
+  if (wc.has_value() && pwc != nullptr) {
     *pwc = wc.value();
     // null terminator -> return 0
     if (wc.value() == L'\0')
diff --git a/libc/src/__support/wchar/mbsrtowcs.cpp b/libc/src/__support/wchar/mbsrtowcs.cpp
new file mode 100644
index 0000000000000..50ef85755941b
--- /dev/null
+++ b/libc/src/__support/wchar/mbsrtowcs.cpp
@@ -0,0 +1,50 @@
+//===-- Implementation for mbsrtowcs function -------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/wchar/mbsrtowcs.h"
+#include "hdr/types/mbstate_t.h"
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/common.h"
+#include "src/__support/error_or.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/wchar/character_converter.h"
+#include "src/__support/wchar/mbrtowc.h"
+#include "src/__support/wchar/mbstate.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace internal {
+
+ErrorOr<size_t> mbsrtowcs(wchar_t *__restrict dst, const char **__restrict src,
+                          size_t len, mbstate *__restrict ps) {
+  size_t i = 0;
+  // Converting characters until we reach error or null terminator
+  for (; i < len; ++i) {
+    wchar_t temp;
+    auto check = internal::mbrtowc(dst == nullptr ? &temp : dst, *src,
+                                   MAX_UTF8_LENGTH, ps);
+    // Encoding error/invalid mbstate
+    if (!check.has_value())
+      return check;
+    // Successfully encoded, check for null terminator
+    if (temp == L'\0' || (dst != nullptr && *dst == L'\0')) {
+      *src = nullptr;
+      return i;
+    }
+    // Set src to point right after the last character converted
+    *src = *src + check.value();
+    // Incrementing destination
+    if (dst != nullptr)
+      ++dst;
+  }
+  return i;
+}
+
+} // namespace internal
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/__support/wchar/mbsrtowcs.h b/libc/src/__support/wchar/mbsrtowcs.h
new file mode 100644
index 0000000000000..5eda23fa7baad
--- /dev/null
+++ b/libc/src/__support/wchar/mbsrtowcs.h
@@ -0,0 +1,29 @@
+//===-- Implementation header for mbsrtowcs function ------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC___SUPPORT_WCHAR_MBSRTOWCS
+#define LLVM_LIBC_SRC___SUPPORT_WCHAR_MBSRTOWCS
+
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/common.h"
+#include "src/__support/error_or.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/wchar/mbstate.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace internal {
+
+ErrorOr<size_t> mbsrtowcs(wchar_t *__restrict dst, const char **__restrict src,
+                          size_t len, mbstate *__restrict ps);
+
+} // namespace internal
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_WCHAR_MBSRTOWCS
diff --git a/libc/src/wchar/CMakeLists.txt b/libc/src/wchar/CMakeLists.txt
index 16664100d42c7..7a27ff8544a1e 100644
--- a/libc/src/wchar/CMakeLists.txt
+++ b/libc/src/wchar/CMakeLists.txt
@@ -78,6 +78,24 @@ add_entrypoint_object(
     libc.src.__support.wchar.mbstate
 )
 
+add_entrypoint_object(
+  mbsrtowcs
+  SRCS
+    mbsrtowcs.cpp
+  HDRS
+    mbsrtowcs.h
+  DEPENDS
+    libc.hdr.types.size_t
+    libc.hdr.types.mbstate_t
+    libc.hdr.types.wchar_t
+    libc.src.__support.common
+    libc.src.__support.macros.config
+    libc.src.__support.wchar.mbsrtowcs
+    libc.src.__support.libc_errno
+    libc.src.__support.wchar.mbstate
+    libc.src.__support.macros.null_check
+)
+
 add_entrypoint_object(
   mbtowc
   SRCS
diff --git a/libc/src/wchar/mbsrtowcs.cpp b/libc/src/wchar/mbsrtowcs.cpp
new file mode 100644
index 0000000000000..3c3140ec1717f
--- /dev/null
+++ b/libc/src/wchar/mbsrtowcs.cpp
@@ -0,0 +1,41 @@
+//===-- Implementation of mbsrtowcs ---------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/wchar/mbsrtowcs.h"
+
+#include "hdr/types/mbstate_t.h"
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/common.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/null_check.h"
+#include "src/__support/wchar/mbsrtowcs.h"
+#include "src/__support/wchar/mbstate.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(size_t, mbsrtowcs,
+                   (wchar_t *__restrict dst, const char **__restrict src,
+                    size_t len, mbstate_t *__restrict ps)) {
+  LIBC_CRASH_ON_NULLPTR(src);
+  static internal::mbstate internal_mbstate;
+  len = dst == nullptr ? SIZE_MAX : len;
+  auto ret = internal::mbsrtowcs(
+      dst, src, len,
+      ps == nullptr ? &internal_mbstate
+                    : reinterpret_cast<internal::mbstate *>(ps));
+  if (!ret.has_value()) {
+    // Encoding failure
+    libc_errno = ret.error();
+    return -1;
+  }
+  return ret.value();
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/wchar/mbsrtowcs.h b/libc/src/wchar/mbsrtowcs.h
new file mode 100644
index 0000000000000..f8d4cc26e63ae
--- /dev/null
+++ b/libc/src/wchar/mbsrtowcs.h
@@ -0,0 +1,24 @@
+//===-- Implementation header for mbsrtowcs -------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_WCHAR_MBSRTOWCS_H
+#define LLVM_LIBC_SRC_WCHAR_MBSRTOWCS_H
+
+#include "hdr/types/mbstate_t.h"
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+size_t mbsrtowcs(wchar_t *__restrict dst, const char **__restrict src,
+                 size_t len, mbstate_t *__restrict ps);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_WCHAR_MBSRTOWCS_H
diff --git a/libc/test/src/wchar/CMakeLists.txt b/libc/test/src/wchar/CMakeLists.txt
index bf16fdd7f8c4d..44f0e7238012b 100644
--- a/libc/test/src/wchar/CMakeLists.txt
+++ b/libc/test/src/wchar/CMakeLists.txt
@@ -39,6 +39,20 @@ add_libc_test(
     libc.test.UnitTest.ErrnoCheckingTest
 )
 
+add_libc_test(
+  mbsrtowcs_test
+  SUITE
+    libc_wchar_unittests
+  SRCS
+    mbsrtowcs_test.cpp
+  DEPENDS
+    libc.src.__support.libc_errno
+    libc.src.string.memset
+    libc.src.wchar.mbsrtowcs
+    libc.hdr.types.mbstate_t
+    libc.hdr.types.wchar_t
+)
+
 add_libc_test(
   mbtowc_test
   SUITE
diff --git a/libc/test/src/wchar/mbsrtowcs_test.cpp b/libc/test/src/wchar/mbsrtowcs_test.cpp
new file mode 100644
index 0000000000000..336da37d158b4
--- /dev/null
+++ b/libc/test/src/wchar/mbsrtowcs_test.cpp
@@ -0,0 +1,149 @@
+//===-- Unittests for mbsrtowcs -------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "hdr/types/wchar_t.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/wchar/mbstate.h"
+#include "src/string/memset.h"
+#include "src/wchar/mbsrtowcs.h"
+#include "test/UnitTest/ErrnoCheckingTest.h"
+#include "test/UnitTest/Test.h"
+
+using LlvmLibcMBSRToWCSTest = LIBC_NAMESPACE::testing::ErrnoCheckingTest;
+
+TEST_F(LlvmLibcMBSRToWCSTest, OneByteOneCharacter) {
+  mbstate_t *mb;
+  LIBC_NAMESPACE::memset(&mb, 0, sizeof(mbstate_t));
+  const char *ch = "A";
+  wchar_t dest[2];
+  size_t n = LIBC_NAMESPACE::mbsrtowcs(dest, &ch, 2, mb);
+  ASSERT_ERRNO_SUCCESS();
+  ASSERT_TRUE(dest[0] == L'A');
+  ASSERT_TRUE(dest[1] == L'\0');
+  // Should not count null terminator in number
+  ASSERT_EQ(static_cast<int>(n), 1);
+  // Should set ch to nullptr after reading null terminator
+  ASSERT_EQ(ch, nullptr);
+}
+
+TEST_F(LlvmLibcMBSRToWCSTest, MultiByteOneCharacter) {
+  const char *src = "\xf0\x9f\x98\xb9"; // laughing cat emoji 😹
+  wchar_t dest[2];
+  size_t n = LIBC_NAMESPACE::mbsrtowcs(dest, &src, 2, nullptr);
+  ASSERT_ERRNO_SUCCESS();
+  ASSERT_EQ(static_cast<int>(dest[0]), 128569);
+  ASSERT_TRUE(dest[1] == L'\0');
+  // Should not count null terminator in number
+  ASSERT_EQ(static_cast<int>(n), 1);
+  // Should set ch to nullptr after reading null terminator
+  ASSERT_EQ(src, nullptr);
+}
+
+TEST_F(LlvmLibcMBSRToWCSTest, MultiByteTwoCharacters) {
+  // Two laughing cat emojis "😹😹"
+  const char *src = "\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9";
+  wchar_t dest[3];
+  size_t n = LIBC_NAMESPACE::mbsrtowcs(dest, &src, 3, nullptr);
+  ASSERT_ERRNO_SUCCESS();
+  ASSERT_EQ(static_cast<int>(dest[0]), 128569);
+  ASSERT_EQ(static_cast<int>(dest[1]), 128569);
+  ASSERT_TRUE(dest[2] == L'\0');
+  // Should not count null terminator in number
+  ASSERT_EQ(static_cast<int>(n), 2);
+  // Should set ch to nullptr after reading null terminator
+  ASSERT_EQ(src, nullptr);
+}
+
+TEST_F(LlvmLibcMBSRToWCSTest, MixedNumberOfBytes) {
+  // 'A', sigma symbol 'Σ', recycling symbol '♻', laughing cat emoji '😹'
+  const char *src = "A\xce\xa3\xe2\x99\xbb\xf0\x9f\x98\xb9";
+  wchar_t dest[5];
+  size_t n = LIBC_NAMESPACE::mbsrtowcs(dest, &src, 5, nullptr);
+  ASSERT_ERRNO_SUCCESS();
+  ASSERT_EQ(static_cast<char>(dest[0]), 'A');
+  ASSERT_EQ(static_cast<int>(dest[1]), 931);
+  ASSERT_EQ(static_cast<int>(dest[2]), 9851);
+  ASSERT_EQ(static_cast<int>(dest[3]), 128569);
+  ASSERT_TRUE(dest[4] == L'\0');
+  // Should not count null terminator in number
+  ASSERT_EQ(static_cast<int>(n), 4);
+  // Should set ch to nullptr after reading null terminator
+  ASSERT_EQ(src, nullptr);
+}
+
+TEST_F(LlvmLibcMBSRToWCSTest, ReadLessThanStringLength) {
+  // Four laughing cat emojis "😹😹😹😹"
+  const char *src =
+      "\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9";
+  const char *check = src;
+  wchar_t dest[3];
+  size_t n = LIBC_NAMESPACE::mbsrtowcs(dest, &src, 3, nullptr);
+  ASSERT_ERRNO_SUCCESS();
+  // Should have read 3 emojis
+  ASSERT_EQ(static_cast<int>(n), 3);
+  ASSERT_EQ(static_cast<int>(dest[0]), 128569);
+  ASSERT_EQ(static_cast<int>(dest[1]), 128569);
+  ASSERT_EQ(static_cast<int>(dest[2]), 128569);
+  // src should now point to the 4th cat emoji aka 13th byte
+  ASSERT_EQ((check + 12), src);
+}
+
+TEST_F(LlvmLibcMBSRToWCSTest, InvalidFirstByte) {
+  // 0x80 is invalid first byte of mb character
+  const char *src =
+      "\x80\x9f\x98\xb9\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9";
+  wchar_t dest[3];
+  size_t n = LIBC_NAMESPACE::mbsrtowcs(dest, &src, 3, nullptr);
+  // Should return error and set errno
+  ASSERT_EQ(static_cast<int>(n), -1);
+  ASSERT_ERRNO_EQ(EILSEQ);
+}
+
+TEST_F(LlvmLibcMBSRToWCSTest, InvalidMiddleByte) {
+  // The 7th byte is invalid for a 4 byte character
+  const char *src =
+      "\xf0\x9f\x98\xb9\xf0\x9f\xf0\xb9\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9";
+  wchar_t dest[3];
+  size_t n = LIBC_NAMESPACE::mbsrtowcs(dest, &src, 5, nullptr);
+  // Should return error and set errno
+  ASSERT_EQ(static_cast<int>(n), -1);
+  ASSERT_ERRNO_EQ(EILSEQ);
+}
+
+TEST_F(LlvmLibcMBSRToWCSTest, NullDestination) {
+  // Four laughing cat emojis "😹😹😹😹"
+  const char *src =
+      "\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9";
+  size_t n = LIBC_NAMESPACE::mbsrtowcs(nullptr, &src, 2, nullptr);
+  ASSERT_ERRNO_SUCCESS();
+  // Null destination should ignore len and read till end of string
+  ASSERT_EQ(static_cast<int>(n), 4);
+}
+
+TEST_F(LlvmLibcMBSRToWCSTest, InvalidMBState) {
+  mbstate_t *mb;
+  LIBC_NAMESPACE::internal::mbstate inv;
+  inv.total_bytes = 6;
+  mb = reinterpret_cast<mbstate_t *>(&inv);
+  // Four laughing cat emojis "😹😹😹😹"
+  const char *src =
+      "\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9\xf0\x9f\x98\xb9";
+  wchar_t dest[3];
+  size_t n = LIBC_NAMESPACE::mbsrtowcs(dest, &src, 3, mb);
+  // Should fail from invalid mbstate
+  ASSERT_EQ(static_cast<int>(n), -1);
+  ASSERT_ERRNO_EQ(EINVAL);
+}
+
+#if defined(LIBC_ADD_NULL_CHECKS) && !defined(LIBC_HAS_SANITIZER)
+TEST_F(LlvmLibcMBSRToWCSTest, NullSource) {
+  // Passing in a nullptr source should crash the program
+  EXPECT_DEATH([] { LIBC_NAMESPACE::mbsrtowcs(nullptr, nullptr, 1, nullptr); },
+               WITH_SIGNAL(-1));
+}
+#endif // LIBC_HAS_ADDRESS_SANITIZER