Abstract. This paper examines the leadership of extreme action teams—teams whose highly skilled members cooperate to perform urgent, unpredictable, interdependent, and highly consequential tasks while simultaneously coping with frequent changes in team composition and training their teams’ novice members. Our qualitative investigation of the leadership of extreme action medical teams in an emergency trauma center revealed a hierarchical, deindividualized system of shared leadership. At the heart of this system is dynamic delegation: senior leaders’ rapid and repeated delegation of the active leader- ship role to and withdrawal of the active leadership role from more junior leaders of the team. Our findings suggest that dynamic delegation enhances extreme action teams’ ability to perform reliably while also building their novice team members’ skills. We highlight the contingencies that guide senior leaders’ delegation and withdrawal of the active leadership role, as well as the values and structures that motivate and enable the shared, ongoing practice of dynamic delegation. Further, we suggest that extreme action teams and other “improvisational” organizational units may achieve swift coordination and reliable performance by melding hierarchical and bureaucratic role-based structures with flexibility-enhancing processes. The insights emerging from our findings at once extend and challenge prior leadership theory and research, paving the way for further theory development and research on team leadership in dynamic settings.