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GoldSrc, or Goldsource, is the retronym used internally by Valve Software to refer to the heavily modified Quake Engine that powers their science fiction first-person shooter Half-Life (1998).

GoldSrc is a modified version of the QuakeWorld engine codebase, which in turn is a development of the Quake engine codebase. Some minor fixes from the Id Tech 2 engine were incorporated as it was developed. GoldSrc is able to render in two APIs − OpenGL and Direct3D.

The successor of the GoldSrc engine is the Source Engine which powers Half-Life 2. While the engine has no official name, in the months before the release of Half-Life, many computing magazines described the engine as being based upon "Quake Unified Technology".