FOMOD is an extension given to files used to install mods for games developed by Bethesda Game Studios, such as Fallout and Elder Scrolls. These files are packed into ZIP or RAR archives along with other files needed to install the modification. FOMOD are files responsible for the correct installation of the modification. This allows you to add additional functionality to the game.

FOMOD files are supported by the Fallout mod manager (FOMM) and Nexus Mod Manager (NMM) tools. These managers are used to install mods in the game.