This chapter provides the tools—both concepts and theories—used to classify and study groups. It introduces a social psychological view of groups, specifically focuses on the forces that unify a group and define the behavior of its members. The chapter discusses conformity as related to group norms, but how is conformity linked to other topics related to groups, including cohesion, goals, and intergroup conflict? How might making these connections enhance our understanding of conformity and groups?" Group cohesion refers to the extent to which members of a group desire to remain in a group and resist leaving it. The term goal isomorphism refers to a state in which group goals and individual goals are compatible in the sense that actions leading to group goals also lead to the attainment of individual goals. Group norms coordinate activity among members, provide a frame of reference that enables members to interpret their environment, and define the common identity of group members.