The chapter begins by examining how groups form and socialise members, and the forces of conformity that sustain existing norms. We then consider the emergence of differentiation and innovation, exploring how processes of minority influence and dissent challenge conformity. The chapter then explores the impact of contested norms, particularly in systems of inequality, and considers how these norms are challenged and transformed under more repressive and open regimes. This chapter also explores power, repression, agency and resistance, and how reinterpretations of classical studies by Milgram and Zimbardo are now understood through the lens of social identity theory. The transmission of norms between groups is discussed, alongside the entrepreneurs of identity who mobilise advantaged groups to support disadvantaged groups. This chapter makes a transition from traditional theories of intergroup relations to new paradigms that emphasise the fluidity of norms, the role of emerging leadership, and the transformative potential of identity in group dynamics.