Rephrasing the words of Lerner and Villarruel (1996, p. 130), adolescence is a period about which much is known, but little has been explained. There is no shortage of descriptions of specific characteristics of cognition, personality, emotional life, and social behavior of adolescents. Adolescence is associated with the ability to think at the formal-logical level (Inhelder & Piaget, 1955/1958), which leads, in particular, to a qualitatively new level of moral reasoning (Kohlberg, 1981, 1984); with adolescents' search for personal identity (Erikson, 1968); with a the development of new sexual desires and sexual intercourse becoming the major motive of adolescent behavior (Freud, 1920/1965); with a substantially increased role of peer interactions in adolescents' lives (Brown, 1990); and with the period of “storm and stress” characterized by conflicts with parents, mood disruptions, and adolescents' risk behavior (see Arnett, 1999, for an overview). What is missing, however, is a holistic explanation of the reasons for the development of all these neo-formations. Whereas different theories (Erikson, 1968; Freud, 1920/1965; Inhelder & Piaget, 1955/1958) make it possible to explain some of the accomplishments and problems that are typical of the period of adolescence in industrialized societies, none of them gives a holistic explanation of the reasons for all the neo-formations during this period. The neo-Vygotskian approach to the analysis of the period of adolescence is not an exception to this rule.