Using data from 607 subjects organized in 161 teams (84 laboratory teams and 77 organizational field teams), we examined how leader humility influences team interaction patterns, emergent states, and team performance. We developed and tested a theoretical model arguing that when leaders behave humbly, followers emulate their humble behaviors, creating a shared interpersonal team process (collective humility). This collective humility in turn creates a team emergent state focused on progressively striving toward achieving the team's highest potential (collective promotion focus), which ultimately enhances team performance. We tested our model across three studies wherein we manipulated leader humility to test the social contagion hypothesis (Study 1), examined the impact of humility on team processes and performance in a longitudinal team simulation (Study 2), and tested the full model in a multistage field study in a health services context (Study 3). The findings from these lab and field studies collectively supported our theoretical model, demonstrating that leader behavior can spread via social contagion to followers, producing an emergent state that ultimately affects team performance. Our findings contribute to the leadership literature by suggesting the need for leaders to lead by example, and showing precisely how a specific set of leader behaviors influence team performance, which may provide a useful template for future leadership research on a wide variety of leader behaviors.