The main difference between Selenium WebDriver and Selenium RC is the way they interact with the browser.  Selenium RC injects a JavaScript function called "Selenium" into the browser when a page is loaded. This function is then used to drive the browser and perform various actions, such as clicking links and filling out forms. The actions are controlled by a remote server, which receives commands from the test script and passes them to the browser.  Selenium WebDriver, on the other hand, communicates directly with the browser using a native browser driver. This allows it to bypass the JavaScript sandbox and directly manipulate the browser's content and layout. As a result, Selenium WebDriver is generally faster and more efficient than Selenium RC.  In addition to the difference in how they interact with the browser, Selenium WebDriver also offers improved support for modern web browsers and provides a more powerful and flexible API. It is the recommended tool for new projects and is considered to be a superior option to Selenium RC.