In 1946 E. M. Jellinek, on the basis of a questionnaire study of members of Alcoholics Anonymous, first formulated his concept of phases in the drinking history of alcoholics. With the original publication1 of this concept Jellinek outlined a more detailed questionnaire, which in the intervening years has been administered to some 2,000 alcoholics. The elaboration of the phases concept resulting from analysis of these additional materials has been presented by Jellinek in lectures at the Yale Summer School of Alcohol Studies (July 1951 and July 1952) and at the European Seminar on Alcoholism (Copenhagen, October 1951). The summary of these lectures, as published under the auspices of the Alcoholism Subcommittee of the World Health Organization,2 is reproduced here in full.