Body composition is now a popular topic in Japan because most Japanese have become aware that obesity is a serious health problem that increases the risk of developing coronary artery disease, hypertension, diabetes and other problems. This article reviews the current methodology for determining body composition in man. Direct compositional analysis of the human body can only be undertaken through the dissection of fresh human cadavers. However, this direct method cannot be applied to living individuals. Many indirect methods have been developed including densitometry, hydrometry, total body potassium by ^<40>K counting, dual energy X-ray absorptiomety and others. Each method stands on its own scientific assumption. The calculated results, therefore, do not necessarily correspond to each other. Many field methods have also been developed by anthropometric studies measuring skinfold thickness by caliper, the subcutaneous fat layer by ultrasound apparatus, and by bioimpedance analysis. These are easy ways for assessing body composition for both field and clinical use. The current study has tried to improve estimation equations, and for clinical use, the body composition of Japanese from the prepubescent to the aged stage wa assessed by densitometry. Body weight, lean body weight, and fat were found to increase during adolescence, and very great increases were evident in body weight and lean body weight among males. The difference in body weight between males and females after the young adult stage is derived from a differece in lean body weight. The changing pattern of body composition in Japanese was very similar to that reported in British and American populations. The appendix about the books on body composition mentions that some Japanese scientists have written the books by compiling their own data.