Friendship is the most important voluntary relationship in the process of growing up. Various authors have pointed out that the structure of equality in friendship fosters cognitive and affective development such as the ability to coordinate perspectives, empathy and care as well as the sense of self. In particular adolescence can be seen as a crucial achievement in the development of the understanding of the intricate connection between the sense of self and responsibilities in relationship. Monika Keller will exemplify how the meaning of (same sex) close friendship changes in the transition from adolescence relationship connectedness (age 15 years) to late adolescence or early adulthood relationship individuation (age 18/19 years). She will take a cross-cultural view on this process by comparing persons from a Western and an Asian cultural context as well as documenting with longitudinal data that the understanding of close friendship in childhood and adolescence predicts perceived friendship intimacy at age 22 years which functions itself as a predictor of (heterosexual) relationship satisfaction at age of 38 years. The interplay of internal and external factors in this developmental process may also shed light on the question why we grow up.