An attempt is made to summarize the chief generalizations that can be drawn from available evidence on world mortality developments during the last hundred years. Past and prospective trends are compared for three broad groups of populations or approximately those in the West, Eastern and Southern Europe, and Latin America, Africa, and Asia. Two major points of emphasis are that the usual methods of comparing regional changes can usefully be supplemented by other approaches, and that the mortality history of Western nations may prove a highly unsatisfactory guide to future trends elsewhere. The study is based on a nearly complete compilation of the national life tables on record.