Echinococcosis (hydatid disease) is a zoonotic infection of human beings caused by the postlarval metacestode stage of the dog tapeworm, Echinococcus. Hydatid disease is more frequently the result of infection by Echinococcus granulosus and E. multilocularis species, which are more widely prevalent geographically than E. vogeli and E. oligarthus. The epidemiology, biology, and host-parasite relationships of echinococcal infection are discussed, and the clinical consequences of human infection are reviewed with particular emphasis on the pulmonary manifestations of the disease. The utility of serological and radiological techniques in diagnosis and management are reviewed. The efficacy of medical therapy and its relationship to the role of surgical intervention in the management of unilocular (cystic) and multilocular (alveolar) hydatid disease is discussed. Finally, the successes and failures of public health programs to control this zoonosis are noted.