Half-Life 2 (stylized as HλLF-LIFE2) is a first-person shooter video game developed and published by Valve Corporation. The sequel to 1998's Half-Life, it was released in November 2004, following a five-year, $40 million development phase, during which a substantial part of the project was leaked and distributed on the Internet. The game was developed alongside Valve's Steam software and the Source engine.

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Some years after the events of Half-Life, protagonist Gordon Freeman is woken by the enigmatic G-Man to find the world has been taken over by the alien Combine. Joined by allies including resistance fighter Alyx Vance, Gordon searches for a way to free humanity using a variety of weapons, including the object-manipulating gravity gun.

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Like its predecessor, Half-Life 2 received critical acclaim. It was praised for its advanced physics, animation, sound, AI, graphics, and narrative. The game won 39 "Game of the Year" awards and the title of "Game Of The Decade" at the 2012 Spike Video Game Awards, and is widely considered to be one of the greatest and most important video games of all time. Over 6.5 million copies of Half-Life 2 were sold at retail by December 2008, (not including Steam sales); as of February 2011, Half-Life 2 had sold over 12 million copies.