An ASI file contains a mod library used to alter gameplay in select Grand Theft Auto (GTA) games, such as GTA IV and V. It stores customized plugins and scripts referenced by the game that modify aspects of gameplay or add new features.

ASI files are only used by GTA gamers who enjoy modifying aspects of the game. Modders may create their own modifications, then package them in an ASI file to be loaded by a GTA game installed on their own local computer. Or modders may upload the ASI file and share it online to be used by other GTA gamers. In order to load an ASI file in a GTA game, the gamer must install an ASI loader. The ASI loader will then load the custom ASI libraries when GTA boots up. NOTE: Some examples of modifications packaged in ASI files include adding extra missions and trainers, customizing actions by characters and vehicle properties, and moving the locations where vehicles spawn.