Dota 2 is a free-to-play multiplayer online battle arena (MOBA) video game developed and published by Valve Corporation. The game is the stand-alone sequel to Defense of the Ancients (DotA), which was a community-created mod for Blizzard Entertainment's Warcraft III: Reign of Chaos and its expansion pack, The Frozen Throne. Dota 2 is played in matches between two teams of five players, with each team occupying and defending their own separate base on the map. Each of the ten players independently controls a powerful character, known as a "hero", who all have unique abilities and differing styles of play. During a match, the player collects experience points and items for their heroes in order to successfully fight the opposing team's heroes, who are doing the same. A team wins by being the first to destroy a large structure located in the opposing team's base, called the "Ancient", which is guarded by defensive towers.

Development of Dota 2 began in 2009 when IceFrog, the pseudonymous lead designer of the original Defense of the Ancients mod, was hired by Valve to create a modernized sequel. Dota 2 was officially released on Steam for Microsoft Windows, OS X, and Linux-based personal computers in July 2013, following a Windows-only public beta phase that began two years prior. Despite some criticism going towards its steep learning curve and complexity, the game was praised for its rewarding gameplay, production quality, and faithfulness to its predecessor. The game initially used the original Source game engine until it was ported to Source 2 in 2015, making it the first game to use it. Since its release, Dota 2 has been one of the most played games on Steam, with over a million concurrent players at its peak. The popularity of the game 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. The game also allows for the community to create custom game modes, maps, and hero cosmetics, which are uploaded to the Steam Workshop.

Dota 2 has a widespread and active competitive scene, with teams from across the world playing professionally in various leagues and tournaments. Premium Dota 2 tournaments often have prize pools totaling millions of U.S. dollars, the highest of any eSport. The largest of them is known as The International, which is produced annually by Valve and held at the KeyArena in Seattle. Valve also sponsors a tournament format known as the Majors and Minors, which are smaller, more frequently held events that award qualification points for getting directly invited to The International. For most tournaments, media coverage is done by a selection of on-site staff who provide commentary and analysis for the ongoing matches, similar to traditional sporting events. Broadcasts of professional Dota 2 matches are streamed live over the internet, and sometimes simulcast on television networks, with peak viewership numbers in the millions.