Leadership is a process enacted in the context of a shared group membership and leadership effectiveness is contingent on followers' perceptions of the leader as a groupmember. Addressing this role of group membership the social identity theory of leadership puts leader group prototypicality the extent to which the leader is perceived to embody group identity centerstage in leadership effectiveness. I review empirical research in leader group prototypicality concluding there is a robust empirical basis for the key propositions of the social identity theory of leadership. I also identify newer developments that extend and enrich the social identity analysis of leadership including attention to the roles of uncertainty leader fairness leader–follower relationship leader self-perceived prototypicality and leadership of creativity and innovation.