The authors provide an overview of the ACCESS program (Access to Community Care and Effective Services and Supports), which evaluated the integration of service systems and its impact on outcomes for homeless persons with severe mental illness. The ACCESS program provided funds and technical assistance to nine community sites to implement strategies for system change that would promote systems integration. These experimental sites, along with nine comparison sites, also received funds to support outreach and assertive community treatment for 100 clients a year for four years at each site. Data on the implementation of system change strategies were collected from 1994 to 1998 during annual visits to the sites. Data on changes in systems integration were obtained from interviews with key informants from relevant organizations in each community. Client outcome data were obtained at program entry and three and 12 months later from 7,055 program participants across the four annual client cohorts at all sites. Detailed findings from the ACCESS evaluation are presented in two accompanying articles, and overall conclusions are offered in a fourth article