The administration of drugs to whole populations irrespective of disease status is referred to as mass drug administration (MDA). This article describes the administration of antimalarial drugs to whole populations an intervention which has been used as a malaria-control measure for more than 70 years. Recent proposals to eliminate or even to eradicate malaria have led to a renewed interest in mass drug administrations in areas with very high malaria endemicity. Drugs have been administered either directly as a full therapeutic course of treatment or indirectly through the fortification of salt. Mass drug administrations were generally unsuccessful in interrupting transmission but, in some cases, had a marked effect on parasite prevalence and on the incidence of clinical malaria. MDAs are