Dota 2 is a multiplayer online battle arena video game, the stand-alone sequel to the Defense of the Ancients (DotA) Warcraft III: Reign of Chaos and Warcraft III: The Frozen Throne mod. Developed by Valve Corporation, Dota 2 was released as a free-to-play title for Microsoft Windows, OS X and Linux in July 2013, concluding a Windows-only public beta testing phase that began in 2011. The game is available exclusively through Valve's content-delivery platform, Steam.

Dota 2 is played in matches involving two teams of five players, each of which occupies a stronghold at a corner of the map. Each stronghold contains a building called the "Ancient", which the opposite team must destroy to win the match. Each player controls a "Hero" character and focuses on leveling up, collecting gold, acquiring items and fighting against the other team to achieve victory.

Development of Dota 2 began in 2009, when the developer of the DotA mod, IceFrog, was hired by Valve as lead designer. Dota 2 was praised by critics for its gameplay, production quality and faithfulness to its predecessor. However, the game was criticized for its steep learning curve and inhospitable community. Dota 2 has become the most actively played game on Steam, with daily peaks of over 800,000 concurrent players.