diff --git a/.hgignore b/.hgignore
--- a/.hgignore
+++ b/.hgignore
@@ -18,3 +18,4 @@
 
 subinclude:cfastmanifest/.hgignore
 subinclude:linelog/.hgignore
+subinclude:examplerust/.hgignore
diff --git a/examplerust/.hgignore b/examplerust/.hgignore
new file mode 100644
--- /dev/null
+++ b/examplerust/.hgignore
@@ -0,0 +1,2 @@
+rustexamplerust/Cargo.lock
+rustexamplerust/target
diff --git a/examplerust/Makefile b/examplerust/Makefile
new file mode 100644
--- /dev/null
+++ b/examplerust/Makefile
@@ -0,0 +1,31 @@
+# Cargo's depfiles use full paths, so we must include the full path
+# to the rust library.
+DIR := $(dir $(realpath $(firstword $(MAKEFILE_LIST))))
+
+ifeq ($(shell uname),Darwin)
+# On MacOS, we must configure the linker to allow resolution of
+# undefined symbols at runtime.
+LIBSUFFIX := .dylib
+CARGO_ARGS += -C link-args='-Wl,-undefined,dynamic_lookup'
+else
+LIBSUFFIX := .so
+endif
+
+RUSTLIB := $(DIR)rustexamplerust/target/release/librustexamplerust$(LIBSUFFIX)
+
+.PHONY: test
+test: examplerust/rustexamplerust.so
+	hg --config extensions.examplerust=examplerust rust
+
+examplerust/rustexamplerust.so: $(RUSTLIB)
+	cp $< $@
+
+$(RUSTLIB):
+	cd rustexamplerust && cargo rustc --release -- $(CARGO_ARGS)
+
+.PHONY: clean
+clean:
+	$(RM) examplerust/rustexamplerust.so
+	cd rustexamplerust && cargo clean
+
+-include rustexamplerust/target/release/librustexamplerust.d
diff --git a/examplerust/README.md b/examplerust/README.md
new file mode 100644
--- /dev/null
+++ b/examplerust/README.md
@@ -0,0 +1,31 @@
+examplerust
+===========
+
+This is an example extension written in [Rust](https://www.rust-lang.org/).
+The extension adds a single command: `hg rust`, which prints out a short
+text string.  Its purpose is to show how integration of extensions written
+in Rust might occur.
+
+Building
+========
+
+The extension uses [rust-cpython](https://github.com/dgrunwald/rust-cpython)
+to interface between Python and Rust, in much the same way as the CPython API
+is used for extensions written in C.
+
+To build, run `make` in this directory.  This will call `cargo` to compile
+the rust library and then copy it into the `examplerust` extension directory.
+
+Running
+=======
+
+To use the extension, run `hg --config extensions.examplerust=examplerust`
+from this directory.
+
+Implementation Details
+======================
+
+As with the extensions written in C, there is a Python extension, `examplerust`,
+which imports the Rust library, `rustexamplerust`.  The Python extension takes
+care of registering methods with the Mercurial registry, and then delegates the
+execution of the command to the Rust library.
diff --git a/examplerust/examplerust/__init__.py b/examplerust/examplerust/__init__.py
new file mode 100644
--- /dev/null
+++ b/examplerust/examplerust/__init__.py
@@ -0,0 +1,21 @@
+# examplerust.py
+#
+# Copyright 2017 Facebook, Inc.
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+"""example extension written in Rust"""
+
+from . import rustexamplerust
+
+from mercurial import registrar
+
+cmdtable = {}
+command = registrar.command(cmdtable)
+
+@command('rust', [
+    ('w', 'how', None, 'Exactly how cool is rust?'),
+])
+def rust(ui, repo, *args, **kwargs):
+    """Run something in rust to show how cool it is."""
+    return rustexamplerust.rust(ui, repo, *args, **kwargs)
diff --git a/examplerust/rustexamplerust/Cargo.toml b/examplerust/rustexamplerust/Cargo.toml
new file mode 100644
--- /dev/null
+++ b/examplerust/rustexamplerust/Cargo.toml
@@ -0,0 +1,13 @@
+[package]
+name = "rustexamplerust"
+version = "0.1.0"
+authors = ["Facebook Source Control Team <sourcecontrol-dev@fb.com>"]
+
+[lib]
+name = "rustexamplerust"
+crate-type = ["cdylib"]
+
+[dependencies.cpython]
+version = "0.1"
+default-features = false
+features = ["python27-sys", "extension-module-2-7"]
diff --git a/examplerust/rustexamplerust/src/lib.rs b/examplerust/rustexamplerust/src/lib.rs
new file mode 100644
--- /dev/null
+++ b/examplerust/rustexamplerust/src/lib.rs
@@ -0,0 +1,57 @@
+// rustexamplerust/src/lib.rs: Rust interface for examplerust
+//
+// Copyright 2017 Facebook, Inc.
+//
+// This software may be used and distributed according to the terms of the
+// GNU General Public License version 2 or any later version.
+//
+
+#[macro_use]
+extern crate cpython;
+use cpython::exc;
+use cpython::{ObjectProtocol, PyBool, PyDict, PyErr, PyObject, PyResult, PyTuple, Python};
+
+py_module_initializer!(
+    rustexamplerust,
+    initrustexamplerust,
+    PyInit_rustexamplerust,
+    |py, m| {
+        m.add(py, "rust", py_fn!(py, rust(*args, **kwargs)))?;
+
+        Ok(())
+    }
+);
+
+/// Example module function.  This function uses the passed-in
+/// `ui` object to print a status message.
+fn rust(py: Python, args: &PyTuple, kwargs: Option<&PyDict>) -> PyResult<PyObject> {
+
+    // Unpack the values of "ui" and "repo" from `args`.  Since this
+    // function accepts arbitrary keyword arguments, we must unpack all
+    // arguments manually.
+    if args.len(py) != 2 {
+        return Err(PyErr::new::<exc::TypeError, _>(
+            py,
+            "Wrong number of arguments",
+        ));
+    }
+    let ui = args.get_item(py, 0);
+    let _repo = args.get_item(py, 1);
+
+    // Check the value of the "how" item in `kwargs`.  Accessing Python
+    // keyword arguments in Rust is a bit cumbersome.  It is preferable
+    // to unpack arguments like this in the Python wrapper, and pass
+    // them in as primitive types when possible.  This example is
+    // included here for completeness.
+    let how = kwargs
+        .and_then(|x| x.get_item(py, "how"))
+        .and_then(|x| x.cast_as::<PyBool>(py).ok().map(PyBool::is_true));
+
+    if how == Some(true) {
+        ui.call_method(py, "status", ("Rust is very cool!\n",), None)?;
+    } else {
+        ui.call_method(py, "status", ("Rust is cool!\n",), None)?;
+    }
+
+    Ok(py.None())
+}