HIV can be transmitted from mother to child before, during, or after birth, but the relative contribution of each route remains unclear. Indirect evidence suggests that a substantial proportion of transmission occurs late in pregnancy or around the time of delivery. In Europe, the rate of vertical transmission is around 15-20% and is associated with maternal HIV status, mode of delivery and length of time from rupture of membranes, and breastfeeding. A number of interventions to reduce vertical transmission have been suggested including avoidance of breastfeeding, caesarean section delivery, disinfection of the birth canal, passive and active immunization, and anti-retroviral therapy. Several clinical trials to evaluate such approaches are ongoing or being planned. The costs of the various options are likely to limit implementation.