This chapter describes and illustrates the most influential or highly utilized of the methods or paradigms that researchers have employed, identifying the particular understandings for which each is responsible, together with an evaluation of the strengths and limitations of each approach. Researchers have employed observation as a method for studying children in groups since the 1920s. Some of this work focused on individual children or siblings and was carried out by scientifically-minded parents or other interested adults. In view of the foregoing issue, a number of researchers have sought to focus on the memberships, intra-group relationships, and inter- and intra-group dynamics of established groups. Much of this research has focussed on aggression and bullying within peer groups. Research on similarities in behavior among children and adolescents who belong to the same friendship peer groups have been extended to include a wide range of both anti-social and prosocial behaviors.