Vaginal birth after cesarean (VBAC) describes vaginal delivery by a woman who has had a previous cesarean delivery. For most of the 20th century, once a woman had undergone a cesarean delivery, clinicians believed that her future pregnancies required cesarean delivery. Studies from the 1960s suggested that this practice may not always be necessary. In 1980, a National Institutes of Health (NIH) Consensus Development Conference Panel questioned the necessity of routine repeat cesarean deliveries and outlined situations in which VBAC could be considered. The option for a woman with a previous cesarean delivery to have a trial of labor was offered and exercised more often in the 1980s through 1996. Since 1996, however, the number of VBACs has declined, contributing to the overall increase in cesarean delivery (Figure 1). Although we recognize that primary cesarean deliveries are the driving force behind the total cesarean delivery rates, the focus of this report is on trial of labor and repeat cesarean deliveries. A number of medical and nonmedical factors have contributed to this decline in the VBAC rate since the mid-1990s, although many of these factors are not well understood. A significant medical factor that is frequently cited as a reason to avoid trial of labor is concern about the possibility of uterine rupture-because an unsuccessful trial of labor, in which a woman undergoes a repeat cesarean delivery instead of a vaginal delivery, has a a higher rate of complications compared to VBAC or elective repeat cesarean delivery. Nonmedical factors include, among other things, restrictions on access to a trial of labor and the effect of the current medical-legal climate on relevant practice patterns. To advance understanding of these important issues, the Eunice Kennedy Shriver National Institute of Child Health and Human Development and the Office of Medical Applications of Research of NIH convened a Consensus Development Conference on March 8-10, 2010. The conference was grounded in the view that a thorough evaluation of the relevant research would help pregnant women and their maternity care providers when making decisions about the mode of delivery after a previous cesarean delivery. Improved understanding of the clinical risks and benefits and how they interact with nonmedical factors also may have important implications for informed decisionmaking and health services planning. The following key questions were addressed by the Consensus Development Conference: 1. What are the rates and patterns of utilization of trial of labor after prior cesarean delivery, vaginal birth after cesarean delivery, and repeat cesarean delivery in the United States? 2. Among women who attempt a trial of labor after prior cesarean delivery, what is the vaginal delivery rate and the factors that influence it? 3. What are the short-and long-term benefits and harms to the mother of attempting trial of labor after prior cesarean versus elective repeat cesarean delivery, and what factors influence benefits and harms? 4. What are the short- and long-term benefits and harms to the baby of maternal attempt at trial of labor after prior cesarean versus elective repeat cesarean delivery, and what factors influence benefits and harms? 5. What are the nonmedical factors that influence the patterns and utilization of trial of labor after prior cesarean delivery? 6. What are the critical gaps in the evidence for decisionmaking, and what are the priority investigations needed to address these gaps?