This study examines the antecedents and outcomes of informal leader emergence in work teams. Drawing upon research in vertical and shared leadership, we hypothesized that the relationship between leader--member exchange (LMX) quality and employees’ emergence as informal leaders is moderated by team shared vision such that there is a positive (negative) LMX—leader emergence relationship for teams with high (low) shared vision. Informal leader emergence, in turn, was expected to relate to higher individual and team performance. Results based on multisource and multimethod data collected at 3 points in time (361 followers in 74 work teams) provided support for these hypotheses. The findings highlight the role played by formal leaders and team shared vision in jointly promoting or inhibiting informal leader emergence and thereby impacting individual performance and team effectiveness.