This document provides an overview of the Selenium 1.0 and 2.0 APIs. Selenium 1.0 uses Selenium Core JavaScript commands and the Selenium RC server and client. Selenium 2.0 uses native browser APIs through the WebDriver and Selenium client library. The document compares Selenium 1.0 and 2.0 on real-life browser interaction simulation and test speed, with Selenium 2.0 providing better simulation and performance.