Today, nonprofit leaders operate in a context of blurred boundaries between the nonprofit and for-profit sectors, prompting them to engage in managerialism. Managerialism has advantages but is also among the many sources of mission drift. Philip Selznick once proposed a style of leadership, called institutional leadership, that directly addresses the risk of mission drift. Despite the importance of institutional leadership in today's era of managerialism, the concept has been underexamined in the literature. Through ethnographic fieldwork with a cohort of nonprofit leaders, I develop a framework of practices leaders can use to maintain mission integrity. My findings reveal that institutional leadership can be a collective endeavor enacted not only by the board and executives but also by staff and other stakeholders. To prevent mission drift, leaders in the study used practices related to mission reflexivity, involvement gatekeeping, enabling stakeholders, building constraints, and encouraging resistance.