Without unique missions to serve a public purpose, nonprofits have no justification to exist. Much of the focus on mission in scholarship centers on concerns with mission drift and pressures from external actors. Yet internal dynamics may be just as important in developing a common mission and the coherent activities pursuing it. This research identifies the structural forces shaping organizational members' individual mission conceptions and leading them to emulate and converge around a shared dominant conception. We apply the concept of institutional isomorphism to 104 interviews conducted with staff, managers, board members, and volunteers from 14 human services nonprofits and explain the isomorphic pathways of individuals adopting dominant mission conceptions. Employing qualitative comparative analysis, we analyze the interviews capturing various combinations of individual backgrounds, motivations for joining the organization, and language used to share the mission with others. We find the presence of seven isomorphic pathways leading nonprofit professionals to adopt the dominant interpretations.