Team Fortress 2 (TF2) is a multiplayer first-person shooter game developed and published by Valve Corporation in 2007. It is the sequel to the 1996 Team Fortress mod for Quake and its 1999 remake, Team Fortress Classic. The game was released in October 2007 as part of The Orange Box for Microsoft Windows and the Xbox 360, and was ported to the PlayStation 3 in December 2007. It was released as a standalone game for Windows in April 2008, and updated to support macOS in June 2010 and Linux in February 2013. It was made free-to-play in June 2011, and is distributed online through Valve's digital retailer, Steam.

Players join one of two teams—RED and BLU—and choose one of nine character classes to play as in game modes such as capture the flag and king of the hill. Its development was led by John Cook and Robin Walker, the developers of the original Team Fortress mod. Team Fortress 2 was announced in 1998 under the name Team Fortress 2: Brotherhood of Arms. Initially, the game had more realistic, militaristic visuals and gameplay, but this changed over the protracted nine years of development. After Valve released no information for six years, Team Fortress 2 regularly featured in Wired News's annual vaporware list. Finally released on the Source game engine in 2007, Team Fortress 2 preserved much of the core class-based gameplay of its predecessors while featuring an overhauled, cartoon-like visual style influenced by the works of J. C. Leyendecker, Dean Cornwell, and Norman Rockwell, alongside an increased focus on the visual and verbal characterization of its playable classes and what the developers have described as a 1960s spy film aesthetic.

Team Fortress 2 has received critical acclaim for its art direction, gameplay, humor, and use of character in a wholly multiplayer game, and since its release has been referred to as one of the greatest video games ever created. The game continues to receive official Valve server support as of 2024, in addition to new content being released on a seasonal basis in the form of submissions made through the Steam Workshop. Since becoming free-to-play, the game's main source of revenue is microtransactions for in-game cosmetics. A 'drop system' was also added and refined, allowing free-to-play users to periodically receive in-game equipment and items. Though the game has had an unofficial competitive scene since its release, both support for official competitive play through ranked matchmaking and an overhauled casual experience were added in July 2016. From early 2020 to mid-2024, cheating bots overrunning Valve’s official matchmaking servers led to fans holding several online protests, and eventually Valve adding new policies regarding game bans.