The various means of delivering essential obstetric services are described for settings in which the maternal mortality ratio is relatively low. This review yields four basic models of care, which are best described by organizational characteristics relating to where women give birth and who performs deliveries. In Model 1, deliveries are conducted at home by a community member who has received brief training. In Model 2, delivery takes place at home but is performed by a professional. In Model 3, delivery is performed by a professional in a basic essential obstetric care facility, and in Model 4 all women give birth in a comprehensive essential obstetric care facility with the help of professionals. In each of these models it is assumed that providers do not increase the risk to women, either iatrogenically or through traditional practices. Although there have been some successes with Model 1, there is no evidence that it can provide a maternal mortality ratio under 100 per 100,000 live births. If strong referral mechanisms are in place the introduction of a professional attendant can lead to a marked reduction in the maternal mortality ratio. Countries using Models 2-4, involving the use of professional attendants at delivery, have reduced maternal mortality ratios to 50 or less per 100,000. However, Model 4, although arguably the most advanced, does not necessarily reduce the maternal mortality ratio to less than 100 per 100,000. It appears that not all countries are ready to adopt Model 4, and its affordability by many developing countries is doubtful. There are few data making it possible to determine which configuration with professional attendance is the most cost-effective, and what the constraints are with respect to training, skill maintenance, supervision, regulation, acceptability to women, and other criteria. A successful transition to Models 2-4 requires strong links with the community through either traditional providers or popular demand.