The general assumption is that multipartner alliances are increasingly favored by firms as means of creating larger pools of shared resources and capabilities. Yet, extant literature has hardly moved beyond anecdotal evidence to systematically address the mechanisms driving their configuration and performance. This study is a step toward clarifying important unknowns about multipartner alliances by proposing and testing a model of multipartner alliance performance that involves two key mediating mechanisms, i.e., alliance scale and scope, that may explain how higher performance is achieved in these increasingly popular forms of organizing interorganizational efforts. The empirical context of the study is the motion picture industry where multipartner alliances have become exceedingly popular in recent decades. Empirical results partially support our proposed theory by demonstrating that alliance scale but not alliance scope mediates the relationship between the number of partners and alliance performance. Our results hold important implications for the growing literature on multipartner alliances.