diff --git a/libc/docs/gpu_mode.rst b/libc/docs/gpu_mode.rst
new file mode 100644
--- /dev/null
+++ b/libc/docs/gpu_mode.rst
@@ -0,0 +1,168 @@
+.. _GPU_mode:
+
+==============
+GPU Mode
+==============
+
+.. include:: check.rst
+
+.. contents:: Table of Contents
+  :depth: 4
+  :local:
+
+.. note:: This feature is very experimental and may change in the future.
+
+The *GPU* mode of LLVM's libc is an experimental mode used to support calling
+libc routines during GPU execution. The goal of this project is to provide
+access to the standard C library on systems running accelerators. To begin using
+this library, build and install the ``libcgpu.a`` static archive following the
+instructions in :ref:`building_gpu_mode` and link with your offloading
+application.
+
+.. _building_gpu_mode:
+
+Building the GPU library
+========================
+
+LLVM's libc GPU support *must* be built using the same compiler as the final
+application to ensure relative LLVM bitcode compatibility. This can be done
+automatically using the ``LLVM_ENABLE_RUNTIMES=libc`` option. Furthermore,
+building for the GPU is only supported in :ref:`fullbuild_mode`. To enable the
+GPU build, set the target OS to ``gpu`` via ``LLVM_LIBC_TARGET_OS=gpu``. By
+default, ``libcgpu.a`` will be built using every supported GPU architecture. To
+restrict the number of architectures build, set ``LLVM_LIBC_GPU_ARCHITECTURES``
+to the list of desired architectures or use ``all``. A typical ``cmake``
+configuration will look like this:
+
+.. code-block:: sh
+
+  $> cd llvm-project  # The llvm-project checkout
+  $> mkdir build
+  $> cd build
+  $> cmake ../llvm -G Ninja                                \
+     -DLLVM_ENABLE_PROJECTS="clang;lld;compiler-rt"        \
+     -DLLVM_ENABLE_RUNTIMES="libc;openmp"                  \
+     -DCMAKE_BUILD_TYPE=<Debug|Release>  \ # Select build type
+     -DLLVM_LIBC_FULL_BUILD=ON           \ # We need the full libc
+     -DLLVM_LIBC_TARGET_OS=gpu           \ # Build in GPU mode
+     -DLLVM_LIBC_GPU_ARCHITECTURES=all   \ # Build all supported architectures
+     -DCMAKE_INSTALL_PREFIX=<PATH>       \ # Where 'libcgpu.a' will live
+  $> ninja install
+
+Since we want to include ``clang``, ``lld`` and ``compiler-rt`` in our
+toolchain, we list them in ``LLVM_ENABLE_PROJECTS``. To ensure ``libc`` is built
+using a compatible compiler and to support ``openmp`` offloading, we list them
+in ``LLVM_ENABLE_RUNTIMES`` to build them after the enabled projects using the
+newly built compiler. ``CMAKE_INSTALL_PREFIX`` specifies the installation
+directory in which to install the ``libcgpu.a`` library along with LLVM.
+
+Usage
+=====
+
+Once the ``libcgpu.a`` static archive has been built in
+:ref:`building_gpu_mode`, it can be linked directly with offloading applications
+as a standard library. This process is described in the `clang documentation
+<https://clang.llvm.org/docs/OffloadingDesign.html>_`. This linking mode is used
+by the OpenMP toolchain, but is currently opt-in for the CUDA and HIP toolchains
+using the ``--offload-new-driver``` and ``-fgpu-rdc`` flags. A typical usage
+will look this this:
+
+.. code-block:: sh
+
+  $> clang foo.c -fopenmp --offload-arch=gfx90a -lcgpu
+
+The ``libcgpu.a`` static archive is a fat-binary containing LLVM-IR for each
+supported target device. The supported architectures can be seen using LLVM's
+objdump with the ``--offloading`` flag:
+
+.. code-block:: sh
+
+  $> llvm-objdump --offloading libcgpu.a
+  libcgpu.a(strcmp.cpp.o):    file format elf64-x86-64
+
+  OFFLOADING IMAGE [0]:
+  kind            llvm ir
+  arch            gfx90a
+  triple          amdgcn-amd-amdhsa
+  producer        <none>
+
+Because the device code is stored inside a fat binary, it can be difficult to
+inspect the resulting code. This can be done using the following utilities:
+
+.. code-block:: sh
+   $> llvm-ar x libcgpu.a strcmp.cpp.o
+   $> clang-offload-packager strcmp.cpp.o --image=arch=gfx90a,file=gfx90a.bc
+   $> opt -S out.bc
+   ...
+
+Supported Functions
+===================
+
+The following functions and headers are supported at least partially on the
+device. Currently, only basic device functions that do not require an operating
+system are supported on the device. Supporting functions like `malloc` using an
+RPC mechanism is a work-in-progress.
+
+ctype.h
+-------
+
+=============  =========
+Function Name  Available
+=============  =========
+isalnum        |check|
+isalpha        |check|
+isascii        |check|
+isblank        |check|
+iscntrl        |check|
+isdigit        |check|
+isgraph        |check|
+islower        |check|
+isprint        |check|
+ispunct        |check|
+isspace        |check|
+isupper        |check|
+isxdigit       |check|
+toascii        |check|
+tolower        |check|
+toupper        |check|
+=============  =========
+
+string.h
+--------
+
+=============   =========
+Function Name   Available
+=============   =========
+bcmp            |check|
+bzero           |check|
+memccpy         |check|
+memchr          |check|
+memcmp          |check|
+memcpy          |check|
+memmove         |check|
+mempcpy         |check|
+memrchr         |check|
+memset          |check|
+stpcpy          |check|
+stpncpy         |check|
+strcat          |check|
+strchr          |check|
+strcmp          |check|
+strcpy          |check|
+strcspn         |check|
+strlcat         |check|
+strlcpy         |check|
+strlen          |check|
+strncat         |check|
+strncmp         |check|
+strncpy         |check|
+strnlen         |check|
+strpbrk         |check|
+strrchr         |check|
+strspn          |check|
+strstr          |check|
+strtok          |check|
+strtok_r        |check|
+strdup
+strndup
+=============   =========
diff --git a/libc/docs/index.rst b/libc/docs/index.rst
--- a/libc/docs/index.rst
+++ b/libc/docs/index.rst
@@ -52,6 +52,7 @@
    usage_modes
    overlay_mode
    fullbuild_mode
+   gpu_mode
 
 .. toctree::
    :hidden: