This chapter examines the development of peer relationships in day care, nursery, school and the community. It explores how children relate to one another, and some of the difficulties that they encounter in their relationships with one another. The chapter considers the controversy around the age at which pre-schoolers are ready to go to nursery or day care, and reports on research into the long-term effects of day care on children’s emotional development. It also considers the importance of friendships from pre-school through to primary and secondary school, as well as the importance of sociometric status within the peer group. The chapter discusses the issue of school bullying and strategies to overcome it. It focuses on the changing nature of relationships with same- and opposite-sex peers. The chapter ends with an anti-social and pro-social behaviour in school and in the community.