diff --git a/api/g3doc/index.md b/api/g3doc/index.md
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@@ -11,3 +11,41 @@
 
 * Memory management, including webrtc's reference counted objects
 * [Thread management](threading_design.md)
+
+## Using WebRTC through the PeerConnection class
+
+The
+[PeerConnectionInterface](https://source.chromium.org/chromium/chromium/src/+/master:third_party/webrtc/api/peer_connection_interface.h?q=webrtc::PeerConnectionInterface)
+class is the recommended way to use the WebRTC library.
+
+It is closely modeled after the Javascript API documented in the [WebRTC
+specification](https://w3c.github.io/webrtc-pc/).
+
+PeerConnections are created using the [PeerConnectionFactoryInterface](https://source.chromium.org/search?q=webrtc::PeerConnectionFactoryInterface).
+
+There are two levels of customization available:
+
+*   Pass a PeerConnectionFactoryDependencies object to the function that creates
+    a PeerConnectionFactory. This object defines factories for a lot of internal
+    objects inside the PeerConnection, so that users can override them.
+    All PeerConnections using this interface will have the same options.
+*   Pass a PeerConnectionInterface::RTCConfiguration object to the
+    CreatePeerConnectionOrError() function on the
+    PeerConnectionFactoryInterface. These customizations will apply only to a
+    single PeerConnection.
+
+Most functions on the PeerConnection interface are asynchronous, and take a
+callback that is executed when the function is finished. The callbacks are
+mostly called on the thread that is passed as the "signaling thread" field of
+the PeerConnectionFactoryDependencies, or the thread that called
+PeerConnectionFactory::CreatePeerConnectionOrError() if no thread is given.
+
+See each class' module documentation for details.
+
+## Using WebRTC components without the PeerConnection class
+
+This needs to be done carefully, and in consultation with the WebRTC team. There
+are non-obvious dependencies between many of the components.
+
+
+