Peers play a crucial role in the establishment of adolescent friendships. While considerable variation exists in the purpose and nature of these friendships, research clearly demonstrates that the basic style of friendship established during the adolescent years is generally replicated in friendships in later life. Thus, the adolescent selection of peer friendship group is critical. For most adolescents, friendships are based on mutual involvement in socially conforming activities conducted primarily with like-minded peers. For some, however, friendships are based on indulgence in non-conforming and delinquent type activities, which in some cases place young people at risk of adverse outcomes. This book provides a substantive understanding of the socio-psychological and cultural processes at play among various adolescent friendships.