Abstract: The present invention generally relate to a retractable utility knife. In one aspect, a knife is provided. The knife comprising a handle and a utility blade having a top edge, a bottom edge, a first side edge and a second side edge. The knife further comprising a blade holder having a lock assembly for holding the utility blade within the blade holder, wherein the lock assembly is movable between a blade lock position and a blade release position and wherein the lock assembly includes a lock member that engages the first side edge in the blade lock position.