Medical research has traditionally been based in academic centers, and the findings are frequently not applicable in community primary care settings. The result is a large gap between the possible and the practical in delivering high-quality primary medical care in the United States. Practice-based research networks (PBRNs), laboratories for primary care clinical research, are the appropriate vehicles for uniting the worlds of community primary care practice and clinical research. Although they have received little attention in the mainstream of clinical and health services research, PBRNs have already reported a variety of findings useful for primary care providers, and these networks have helped to identify key issues in healthcare delivery that affect important outcomes. In this report, we outline the rationale for and history of PBRNs. We describe the organization and work of several productive PBRNs, giving examples of their studies that have changed the standards of modern primary care practice. Finally, we describe a developing electronic process for identifying research questions obtained directly from primary care providers that can be used to focus the national primary care research agenda on questions of clinical relevance and importance. As electronic technologies are fully developed and tested, they will facilitate communication between clinicians and researchers, thereby improving the effectiveness and efficiency of practice-based research.