There are three main versions of Selenium - Selenium 1, Selenium 2, and Selenium 3. Selenium 1 was the original version released in 2006 and included Selenium IDE, RC, and Grid. Selenium 2 was released in 2011 and added WebDriver support. The latest version is Selenium 3, released in 2016, which also uses WebDriver and Grid. A future Selenium 4 version has not yet been released.