This report presents the recommendations of a WHO Expert Committee responsible for updating and revising the Model List of Essential Drugs. The first part describes the criteria for the selection of essential drugs and pharmaceutical dosage forms, and includes discussion of quality assurance, pharmacovigilance, drug utilization studies, drug information and educational activities, and future developments of the model list. In the light of increasing resistance to antimicrobials, particular attention is drawn to the need for and use of reserve antimicrobials. The second part presents the eleventh revised model list, together with details of the changes that have been made, a glossary of terms and an alphabetical index of all the drugs included.