The Homeless I Project represents the successful linking of practice and science in the development, delivery, and evaluation of innovative interventions for substance abuse and homelessness in a community-based setting. Several positive outcomes resulted from the collaboration between university investigators and providers of health care for the homeless. These included a productive research and service delivery collaboration, important project and community linkages, SAGE Publicationstional research and service delivery linkages, service enhancements for homeless persons with substance abuse problems, development of an innovative abstinent-contingent work therapy and housing program, significant client participation rates, effective dissemination of method and results, and continued practice and research. Obstacles and solutions related to integrating science and practice, overcoming community resistance, and maintaining linkages are presented. Suggested applications for linking science and practice are offered. © 2000, Sage Publications. All rights reserved.