Sleep disturbance is a risk factor for various physical and mental disorders, and also for industrial and traffic accidents. Therefore, sleep disturbance is considered to be a serious public health issue. Nationwide epidemiological studies of sleep have been conducted in various countries using samples representative of the general population. In Japan, epidemiological sleep study has been increasing in recent years. The accumulated epidemiological evidence of Japanese sleep behavior or sleep disturbances are as follows: (1) sleep duration gradually became shortened, (2) being female, of younger age, living in an urban environment, unemployed, and having an unhealthy lifestyle were associated with short sleep duration, (3) sleep duration exhibited a U-shaped association with symptoms of depression, (4) sleep duration is closely associated with glucose intolerance and dyslipidemia, (5) the prevalence of insomnia among the adult population was 21.4%, (6) the prevalence of excessive daytime sleepiness among the adult population was 15%, (7) excessive daytime sleepiness is associated with disagreeable sensations in the legs and interruption of sleep by snoring or dyspnea, (8) sleep duration of the Japanese adult population is shorter than that of Europeans, and (9) the prevalence of insomnia among adolescents was 23.5%. These epidemiological findings will contribute toward the development of health promotion activities in the future. Further epidemiological studies are required to clarify the sleep characteristics of the Japanese population.