Human adaptability, as a field of inquiry within human biology, became defined during the research activities of the International Biological Program (IBP) (1964-1974). During this period, research was focused on ecological, physiological, and genetic studies of human populations within the theoretical frameworks of adaptation and evolution. Other defining characteristics of the IBP human adaptability research were standardization of methods, multidisciplinary projects, international cooperation, and a concern with human health issues. Some observers suggest that this research contributed to the ongoing transformation of physical anthropology and related fields from a largely descriptive to an analytical science. During the 25 years between the end of the IBP and the present, a number of research trends have continued: Several new multidisciplinary projects were initiated and completed; a subfield of demography within human biology has matured; nutrition, infant and child growth, and health studies have proliferated; and molecular genetics and DNA analysis have superseded the earlier population genetics. International programs today are geared toward more practical and applied studies with less emphasis on basic science. Continuation of human adaptability research into the 21st century is likely to make contributions in 3 broad areas: population, environment, and health. Productive research is likely to contribute to these 3 areas in the following categories: reproduction, psychosocial stress, life span approaches to health, effects of losses in biodiversity on health, a human biology of poverty, emerging infectious diseases, epidemiology of modernization, evolutionary medicine, and aging. The success of much of this research in its contribution to knowledge will come from the integrated perspectives of a biobehavioral framework of inquiry.