Acquisition Category; a designation for each program based on cost that determines both the level of review that is required by law and the level at which milestone (see below) decision authority rests in DoD. There are four acquisition categories, ACAT I through ACAT IV; the most expensive systems are designated ACAT I. ACAT I programs have two sub-categories: ACAT ID (milestone decision authority is the USD[A&T]); and ACAT IC (milestone decision authority is the DoD Component Head.