This paper is a review and some considerations of studies on adult development. Recently, adult life is regarded as a period of development with the changes of life-cycle and life styles. However, the history of the studies on adult development is comparatively short. Mainly, Epigenetic Scheme by Erikson (1950) built a theoretical base for adult developmental studies, and empirical studies on adult development have been increasing since 1970's, for example Levinson (1978), Gould (1978), Vaillant (1977) and Sheehy (1974). Following points are suggested by these recent studies : (1) there are common developmental process and characteristics in adult life. (2) It is observed that there are some critical periods in psychological development such as middle age crisis or mid-life transition, and late adult transition. On the other hand, the developmental studies on adult identity, gradually increasing after 1980's, produce some important viewpoints to grasp psychological changes in adult lives in its totality.