This qualitative study explores the deinstitutionalization of peacebuilding in Ireland and how the core population of peacebuilding organizations are responding. We document organizational responses to the understudied phenomenon of deinstitutionalization—the weakening and dissipating of an institutionalized set of practices and beliefs. We rigorously map the field and population under study, illustrating the challenge and necessity of delineating a field of actors involved in a complex social process. This research contributes to understanding deinstitutionalization in two ways. First, we illustrate how organizations both adapt to and resist the challenge of deinstitutionalization. Second, organizations can act as custodians of outgoing traditions, turning to their communities and engaging in defensive institutional work, which seems to enhance their organizational survival.