Presenting the broad lines of the action and evolution of the World Health Organization (WHO), this work identifies some of the problems WHO has had to face in the past, and will have to confront in the future. It discusses in detail the historical origins, WHO's objectives, and the evolution of its strategy and programmes. The Organization's structures as well as the problems raised by its decentralization are reviewed, as well as its action in the field of technical co-operation and several of its more important past and present programmes. The general conclusion attempts to envisage the future of the Organization.;The study is based essentially on WHO's official documentation, both open and restricted, and on the personal experience of the main author, a former WHO official.