This study explores how team core self-evaluations (CSE) influence the emergence and effectiveness of shared leadership. Drawing on adaptive leadership theory, we propose that decisions to share leadership responsibilities rather than allocating the role to a single team member are influenced by homogeneity in members' CSE. In addition, we identify team collective identification as an emergent team state that interacts with CSE homogeneity to promote the emergence of shared leadership. We then argue that not all shared leadership teams are equally effective; applying group social capital theory, we propose that team mean CSE strengthens the impact of shared leadership on team performance. Results based on multisource and time-lagged data from 85 project teams provide support for our proposed moderated mediation model. We discuss how our theoretical model extends research on the role of team dispositional composition on the antecedents and consequents of shared leadership and highlight practical implications related to the design, recruitment, and socialization of autonomous work teams.