Community-based participatory research (CBPR) increasingly is being used to study and address environmental justice. This article presents the results of a cross-site case study of four CBPR partnerships in the United States that researched environmental health problems and worked to educate legislators and promote relevant public policy. The authors focus on community and partnership capacity within and across sites, using as a theoretical framework Goodman and his colleagues' dimensions of community capacity, as these were tailored to environmental health by Freudenberg, and as further modified to include partnership capacity within a systems perspective. The four CBPR partnerships examined were situated in New York, California, Oklahoma, and North Carolina and were part of a larger national study. Case study contexts and characteristics, policy-related outcomes, and findings related to community and partnership capacity are presented, with implications drawn for other CBPR partnerships with a policy focus. (Contains 3 tables and 1 figure.)