Most research suggests that nonprofit organizations (NPOs) should professionalize in order to become more efficient. Yet a growing body of literature considers that this approach fails to take into account the original grassroots culture that some NPOs would like to preserve. Our four stages integrative model contributes to this debate in three important ways: first, we suggest that the development of NPOs is characterized by the acquisition of a double nature i.e. social community valuing informal egalitarian participation (stage 1) and professional structure based on formal centralized coordination (stage 2); second, we show that this dual system often leads NPOs to existential crisis (stage 3); third, we conclude that this indetermination requires leaders’ idiosyncratic arbitration (stage 4). We discuss the reasons why, despite institutional conformism, the nonprofit sector remains so diverse and how leaders can become institutional entrepreneurs, deliberately building elements of community within and around the organization.