The genetics of human obesity was reviewed here in terms of studies dealing with body fat and fat distribution. The role of heredity was examined by reviewing genetic disorders in which obesity is a clinical feature. Two kinds of genetic effects were discussed: the additive genetic effect and the genotype-environment interaction effect. Several indicators of body fat exist, including body mass index, amount of subcutaneous fat, percentage body fat, fat mass, regional fat distribution, and subcutaneous fat pattern. A low additive genetic effect of less than 10% of human phenotypic variation is found in body mass index and amount of subcutaneous fat, while percentage body fat, fat mass, fat distribution, and fat patterning are characterized by heritability estimates of about 25%. On the other hand, a recent study demonstrates that there is an important genotype-environment interaction effect in human body fat variation induced by overfeeding. Limitations of current approaches to the study of the genetics of human body fat and obesity are considered and comments are offered concerning promising areas of future research.