This paper describes a study currently underway that uses a collaborative approach to assess organizational capacity to form partnerships around mental health and substance abuse care. Employing many of the principles of community-based participatory research, the study's primary objective is to collaboratively develop a conceptual understanding and generalizable, practical measures of organizational capacity. The intent of this collaborative approach is to increase the rigor and relevance of the assessment framework while strengthening the ability of health partnerships and stakeholders to understand and track community organizational capacity. The study investigators developed an initial model of community dissemination based on the research literatures on organizations and the diffusion of innovations. Through the collaborative process, the specific goals of the project shifted substantially to match the partnership interests and concerns of community agencies. One of the benefits of a collaborative approach has been to use researchers' academic knowledge to catalogue potential factors and the wealth of community coinvestigators' experiential knowledge of interagency dynamics to identify specific relevant dimensions of capacity. This initial exploratory study represents a first step toward developing a general approach to conceptualizing and tracking the organizational capacity of communities. The model and measurement framework may have wider applicability to capacities to partner around and implement a variety of health-related interventions within communities.