Clinicians and the organizations within which they practice play a major role in enabling patient participation in cancer screening and ensuring quality services. Guided by an ecologic framework, the authors summarize previous literature reviews and exemplary studies of breast, cervical, and colorectal cancer screening intervention studies conducted in health care settings. Lessons learned regarding interventions to maximize the potential of cancer screening are distilled. Four broad lessons learned emphasize that multiple levels of factors—public policy, organizational systems and practice settings, clinicians, and patients—influence cancer screening; that a diverse set of intervention strategies targeted at each of these levels can improve cancer screening rates; that the synergistic effects of multiple strategies often are most effective; and that targeting all components of the screening continuum is important. Recommendations are made for future research and practice, including priorities for intervention research specific to health care settings, the need to take research phases into consideration, the need for studies of health services delivery trends, and methods and measurement issues. Cancer 2004. © 2004 American Cancer Society.