MPQ, or MoPaQ, is a proprietary archive format created by Mike O'Brien, the man hailed as Blizzard's multiplayer engine genius, back in 1996 as a general purpose archive for use with Diablo, and named narcissistically for its creator - "Mike O'brien PaCK". The copyrights to it, however, are held by Havas Interactive, Blizzard's parent company. The archive format is used by many Blizzard titles like Diablo, Diablo 2, Starcraft, Warcraft 2: BNE, and a newer version in Warcraft 3 and World of Warcraft.
Libmpq is a library for reading MPQ files which can be easily used in applications. Since version 0.4.0 libmpq includes full API documentation for developers. Libmpq also has D and Python high-level bindings.