Abstract
This chapter examines how individuals select the social groups they choose to join and how these groups, in turn, influence individual behavior and decision-making. Using key concepts from social psychology, we explore three primary factors that guide group selection: (1) perceived similarity and affinity with other group members; (2) the group’s reputation and social standing; (3) the anticipated sense of being accepted within the group. Additionally, we discuss how social groups influence individual decision-making through the enforcement of social norms, i.e., the collectively shared expectations of appropriate behavior within a group. Through this lens, the chapter aims to explore how these psychosocial mechanisms operate across various aspects of life, from romantic and friendship relationships to work and political participation, demonstrating their generalizability across diverse contexts and highlighting the pervasive influence of group dynamics in shaping decision making processes.