Cognitive locks' are ideational path dependencies in policy making (Blyth, 2001). This article argues that one source of cognitive locks is the presence of single party dominant regimes. Single party dominant regimes exist where a single party has managed to control the process of executive formation for an unusually long period of time. Because of their long tenure in executive office, dominant parties are often in positions to implement strong cognitive locks on their political societies. Not all cognitive locks are the same, however. Rather, how the dominant party behaved, either as a 'distributional coalition' or as an 'encompassing organization' (Olson, 1982) and how it subsequently incorporated 'voice' (Hirschman, 1970) to accommodate multiple interests, strongly influence the scope of the dominant party's cognitive lock. These observations are utilized in two brief case illustrations derived from well-known cases of single party dominance.