In February 2006 a group of social service executives in the Dutch city of Rotterdam founded what they called the Münchhausen Movement. This movement is an initiative to improve collaboration between public institutions that service vulnerable members of society, such as the homeless, addicts, people with mental health impairments, and frequent recidivists. The members of the Münchhausen Movement explicitly refer to their collaboration as a "Movement." This is a new concept in the world of multiagency collaboration. Coordination of social services is generally seen in terms of public management, organizational innovation, citizenship, or a relational, interpretive effort. This study aims to demonstrate that the concept of a social movement is a useful perspective for understanding and promoting multiagency coordination. This concept is elaborated by using the methods of grounded theory to unravel the initiators of the Münchhausen Movement’s central ideas, values, and practices. This case study results in a critical evaluation of the added value of social movements for multiagency coordination between public institutions., It analyzes the mechanisms, such as trust building, realizing small, but highly visible successes, and value articulation, by which collaboration is achieved. It concludes with the finding that a social movement can contribute to cultural change in fragmented organizational fields and to the enhancement of the density and effectiveness of the professional networks of representatives of the involved organizations but that further dissemination of the movement’s principles and modes of action is essential for its wider success.