Preventing preterm delivery remains one of the great challenges in modern medicine. Preterm birth rates continue to increase and accounted for 12.7 percent of all U.S. births in 2005. The etiology of preterm delivery is unclear, but is likely to be complex and influenced by genetics and environmental factors. Women with previous preterm birth are at increased risk of subsequent preterm delivery and may be candidates for treatment with antenatal progesterone. Fetal fibronectin testing and endovaginal ultrasonography for cervical length are useful for triage. For the patient in preterm labor, only antenatal corticosteroids and delivery in a facility with a level III neonatal intensive care unit have been shown to improve outcomes consistently. Tocolytic agents may delay delivery for up to 48 hours, enabling the administration of antenatal corticosteroids or maternal transfer. Routine use of antibiotics in preterm labor is not indicated except for group B streptococcus prophylaxis or treatment of chorioamnionitis.