Black Mesa is a first-person shooter game developed and published by Crowbar Collective. It is a third-party remake of Half-Life (1998) made in the Source game engine. Originally published as a free mod in September 2012, Black Mesa was approved by Half-Life developers Valve for a commercial release; the first commercial version was published as an early-access version in May 2015, followed by a full release in March 2020 for Windows and Linux.

Black Mesa was developed in response to Half-Life: Source (2005), Valve's port of Half-Life to the Source engine, which lacked new features or improvements. Two teams wanted to improve on the Source remake, and eventually merged to become Crowbar Collective. While they had originally targeted a release by 2009, the team realized they had rushed to this point, and reevaluated their efforts to improve the quality of the remake.

Since then, attention to details, adapting the game to an improved version of the Source engine, and completely reworking the oft-derided final chapters of Half-Life (known as Xen) had lengthened the development efforts of the remake. Due to its long development time, the modification became notable for its delays on the status of its completion. Major changes include reskinned collection of textures, models, and NPCs; a longer runtime; improved level and puzzle design along with challenging enemy artificial intelligence, and additional dialogue and story elements.

The early-access version of Black Mesa received positive reviews, and gained more positive reviews as it was updated and improved. Reviewers praised the gameplay and attention to detail, comparing it to that of an official Valve release, and the improvements to the Xen chapters.