Versions of Selenium

Different versions of Selenium

Selenium IDE

Firefox add-on Selenium IDE allows users to record and re-play user actions in Firefox. It supports exporting the recorded scripts into Selenium RC or Selenium WebDriver code.

Selenium 1 / Selenium RC

Also known as Selenium 1 incorrectly, Selenium Remote Control is the first version of Selenium API, which was generally known as "Selenium" without any version suffixes at the time. After the release of second generation of Selenium, it started to be called with version number or name in order to be distinguishable from the new API. It is now officially deprecated but still released within Selenium WebDriver library for backward compatibility purpose.

Selenium 2 / Selenium WebDriver

Selenium 2, a.k.a. Selenium WebDriver, is the latest API in Selenium project, which replaces Selenium RC with fundamentally different mechanisms and dominates web UI automation market right now.

Selenium 3

The next release of Selenium project, which is only in staging at the time of writing. One possible major change would be breaking the backward compatibility, i.e. Selenium RC will be no longer a part of Selenium release. More details can be followed and discussed in this post on Selenium Developers' forum.

WebDriver

The term "WebDriver" might have different meanings in various contexts.

Synonym for Selenium WebDriver / Selenium 2.

A tool called "WebDriver" which was created independently then got merged into Selenium.

Comparison of Selenium versions

Version	Version	Comparison
Selenium 1	Selenium RC	Essentially the same thing. Selenium 1 has never been an official name, but is commonly used in order to distinguish between versions.
Selenium 2	Selenium WebDriver	Essentially the same thing. The term "Selenium WebDriver" is now more commonly used.
Selenium RC	Selenium WebDriver	Selenium RC is the predecessor of Selenium WebDriver. It has been deprecated and now released inside Selenium WebDriver for backward compatibility.
Selenium IDE	Selenium RC/WebDriver	Selenium IDE is a recording tool for automating Firefox, with the ability to generate simple RC/WebDriver code. Selenium RC/WebDriver are frameworks to automate browsers diagrammatically.
Selenium Grid	Selenium WebDriver	Selenium Grid is a tool to execute Selenium tests in parallel on different machines. Selenium WebDriver is the core library to drive web browsers on a single machine.

Selenium Relationships

Selenium RC Server / Selenium Server

Selenium RC Server was the Java-based package to run Selenium RC tests. With the release of Selenium WebDriver, Selenium (Standalone) Server was introduced as the super-set of the previous version, so that tests can be executed remotely in Selenium Grid mode. For Selenium WebDriver tests that are running locally, Selenium Server is not required.