This document discusses the two main APIs used by WordPress - XML-RPC and AtomPub. XML-RPC uses XML over HTTP POST to transmit basic data types and allows for functions like metaWeblog.getPost. AtomPub uses HTTP methods to interact with Atom feeds and individual posts and comments. It provides a standardized way to interact with content repositories. The document also outlines tools for working with the WordPress APIs like the iPhone app and XML-RPC libraries for developers.