Social relationships in early adolescence are centered in the peer group. Group values guide individual behaviour. Acceptance by peers is critical to self-esteem. Most peer relationships are still same-sex. Young adolescents become interested in sexual relationships, but most contact is through groups. Some youth may begin to experiment with sexual behaviour, but many early adolescents are not sexually active with other youth. Social roles are still largely defined by external sources. During middle and late adolescence, values become individualized and internalized after careful consideration and independent thought. Friends are more often selected on personal characteristics and mutual interests. The peer group declines in importance, individual friendships are strengthened, and more youth "date" in one-on-one relationships. The youth experiments with social roles and explores options for career choice.