diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
new file mode 100644
index 0000000..a56a3eb
--- /dev/null
+++ b/CONTRIBUTING.md
@@ -0,0 +1,29 @@
+This repository contains example Firefox [WebExtensions](https://developer.mozilla.org/en-US/Add-ons/WebExtensions).
+
+We're really happy to accept contributions, either as new examples or as
+improvements to the existing examples. This file lists some general guidelines
+to help contributors write useful examples.
+
+The examples are intended to demonstrate how to use the WebExtensions technology,
+particularly [APIs](https://developer.mozilla.org/en-US/Add-ons/WebExtensions/API),
+but also [manifest.json keys](https://developer.mozilla.org/en-US/Add-ons/WebExtensions/manifest.json)
+and more general techniques such as internationalization or message passing.
+
+More specifically, they're intended to be referenced from the MDN documentation
+for WebExtensions. So, for example, we'll expect the reference page for
+`tabs.executeScript()` to link to some examples that demonstrate how to use this
+API.
+
+So examples should:
+
+* have a clear function, that's easy to explain and understand
+* focus on demonstrating how to use the WebExtension technology, minimizing any
+complex logic that's extraneous to the WebExtension technology itself
+* demonstrate good-practice use of the technology, even at the expense of extra
+complexity
+* include useful optional manifest.json keys: `description` and `homepage_url`
+
+Finally, note that the examples are all made available under the
+[Mozilla Public License 2.0](https://github.com/mdn/webextensions-examples/blob/master/LICENSE),
+so any contributions must be
+[compatible with that license](https://www.mozilla.org/en-US/MPL/license-policy/).