Preterm labor occurs in up to 10% of all births but is associated with 85% of perinatal deaths in otherwise normal babies. Elucidation of the mechanisms involved in normal labor is an important prerequisite for the development of effective therapeutic strategies to prevent and treat preterm labor. Prostaglandins are important in human parturition. They have been used extensively for induction of labor. Prevention of their formation with prostaglandin synthase inhibitors can delay delivery in preterm labor. Nevertheless, the functional activity of prostaglandins in gestational tissues is complex. There are numerous classes of prostaglandins that act on many different prostanoid receptors. Receptor subtypes, even within the same class, are coupled to various second messengers and may thus be stimulatory or inhibitory. Alternate splicing leads to additional diversity. Within this complex background, the tissue-, gestation-, and labor-associated changes in prostaglandins and their receptors are reviewed.