Colorectal cancer (CRC) screening has been supported by strong research evidence and recommended in clinical practice guidelines for more than a decade. Yet screening rates in the United States remain low, especially relative to other preventable diseases such as breast and cervical cancer. To understand the reasons, the National Cancer Institute and Agency for Healthcare Research and Quality sponsored a review of CRC screening implementation in primary care and a program of research funded by these organizations. The evidence base for improving CRC screening supports the value of a New Model of Primary Care Delivery: 1. a team approach, in which responsibility for screening tasks is shared among other members of the practice, would help address physicians' lack of time for preventive care; 2. information systems can identify eligible patients and remind them when screening is due; 3. involving patients in decisions about their own care may enhance screening participation; 4. monitoring practice performance, supported by information systems, can help target patients at increased risk because of family history or social disadvantage; 5. reimbursement for services outside the traditional provider-patient encounter, such as telephone and e-mail contacts, may foster enhanced screening delivery; 6. training opportunities in communication, cultural competence, and use of information technologies would improve provider competence in core elements of screening programs. Improvement in CRC screening rates largely depends on the efforts of primary care practices to implement effective systems and procedures for screening delivery. Active engagement and support of practices are essential for the enormous potential of CRC screening to be realized.