The prevention of preterm birth may be the most important problem facing maternity care providers. Preterm birth occurs in 10% of all births in the United States and is associated with 83% of perinatal deaths not caused by congenital anomalies. This article reviews the anatomy and physiology of the uterus, the physiology of uterine contractions, the initiation of labor, the etiology of preterm labor, risk factors and risk scoring for preterm labor, and the diagnosis and management of preterm labor. The components of a preterm birth prevention program are described, and recommendations for clinical practice are made.