The paper examines the methodological issues involved in the relationship of adult education to adult development. The practice of adult education during the past 25 years has been built upon a series of assumptions derived from theoretical fragments regarding lifelong development. Considering the theoretical base of adult development, however, very little has been verified and set within a sound, comprehensive framework of the total life-span. Any comprehensive theory of adult development must take into consideration not only the psychological and social factors of human life, but also the physiological, economic, vocational, religious, and political factors which affect contemporary life. Of the three traditional research methodologies, the cross-sectional, the cross-sequential, and the longitudinal designs, the longitudinal has proven the most effective technique for studying developmental change. Within the latter methodology, the technique of biography has proven effective because it provides primary data across generations and even epochs. Whichever research design is selected for the study of life-span development, the researcher must effectively manipulate the factors of change and sameness which define the developing individual. In order to do so it is necessary to learn more about the developmental stages through which the individual proceeds. (JR)