Recognition of preterm birth as the major underlying cause of infant mortality in the United States has placed responsibility for prevention in the hands of obstetrician–gynecologists. The advent of effective methods to identify and treat women with increased risk is a major advance that will alter the focus of prenatal care. Adoption of research findings into clinical practice, never an easy task, will be particularly challenging for efforts to reduce the risk of preterm birth. Historical risk factors for preterm birth are numerous and variably defined. Measurement of the length of the cervix with ultrasonography requires unique personnel and facilities. Care algorithms exist but lack the detailed information that comes with experience. This review offers perspective and detail to aid health care practitioners in developing a prematurity prevention strategy appropriate to their practice population.