The purpose of this article is to review the evidence regarding the effectiveness of continuous support provided by a trained laywoman (doula) during childbirth on obstetrical and postpartum outcomes. Twelve individual randomized trials have compared obstetrical and postpartum outcomes between doula-supported women and women who did not receive doula support during childbirth. Three meta-analyses, which used different approaches, have been performed on the results of the clinical trials. Emotional and physical support significantly shortens labor and decreases the need for cesarean deliveries, forceps and vacuum extraction, oxytocin augmentation, and analgesia. Doula-supported mothers also rate childbirth as less difficult and painful than do women not supported by a doula. Labor support by fathers does not appear to produce similar obstetrical benefits. Eight of the 12 trials report early or late psychosocial benefits of doula support. Early benefits include reductions in state anxiety scores, positive feelings about the birth experience, and increased rates of breastfeeding initiation. Later postpartum benefits include decreased symptoms of depression, improved self-esteem, exclusive breastfeeding, and increased sensitivity of the mother to her child's needs. The results of these 12 trials strongly suggest that doula support is an essential component of childbirth. A thorough reorganization of current birth practices is in order to ensure that every woman has access to continuous emotional and physical support during labor.