Traditionally, family firm studies have assumed there is a single family behind the firm. We challenge this assumption and argue that the distinction between multi-founding family firms and single-founding family firms matters. We theorize that multi-founding family firms, based on mutual monitoring among families, have corporate governance advantages (less principal–agent and principal–principal problems) in terms of reduced founder CEO entrenchment and a lower probability of descendent leadership. Furthermore, we argue that multi-founding family firms exhibit higher levels of innovation and performance. Based on U.S. firms during 2001 to 2010, we find robust support for our arguments.