Dota 2 is a free-to-play multiplayer online battle arena (MOBA) video game developed and published by Valve Corporation forMicrosoft Windows, OS X, and Linux. The game is the stand-alone sequel to Defense of the Ancients (DotA), which was a community-created mod for Warcraft III: Reign of Chaos and its expansion pack, The Frozen Throne. Dota 2 is played in matches between two teams that consist of five players, who each occupy their own base on the map. Each player controls a powerful character, known as a "hero", that feature unique abilities and different styles of play. During a match, a player and their team collects experience points, currency, and items for their heroes in order to better fight heroes of the opposing team, attempting to push through their defenses. A team wins by being the first to destroy a large structure located in the opposing team's base, called the "Ancient".

Development of Dota 2 began in 2009 when IceFrog, lead designer of the original Defense of the Ancients mod, was hired by Valve for the same role. Dota 2 was officially released in July 2013, following a Windows-only open beta phase that began two years prior. The game initially used the original Source game engine until it was ported over to Source 2 in 2015, making it the first game to use it. The game also allows for the community to create custom game modes, maps, and cosmetics for the heroes, which are then uploaded to the Steam Workshop. Dota 2 is one of the most actively played games on Steam, with peaks of over a million concurrent players, and was praised by critics for its gameplay, production quality, and faithfulness to its predecessor, despite being criticized for its steep learning curve. The popularity of Dota 2 has led to official merchandise being produced for it, including apparel, accessories, and toys, as well as promotional tie-ins to other games and media.

Dota 2 also has a widespread and active competitive scene, with teams from across the world playing professionally in variousleagues and tournaments. Premium Dota 2 tournaments often have prize pools totaling millions of dollars, the highest of any eSport. The largest of them is known as The International, which is hosted by Valve and takes place annually at the KeyArena in Seattle, with Valve also sponsoring smaller, but more frequently held tournaments known as the Majors. Dedicated media coverage of professional tournaments are broadcast live on the internet, and sometimes on television networks, with peak viewership numbers in the millions.