This chapter explores some of the complexities and challenges of understanding adolescence, social norms and gender norms in the development context. It describes a rising interest among policy and programme actors in adolescent girls and gender norms. The chapter outlines how the interplay between individual agency, gender norms and the wider institutional environment restricts girls' agency and their opportunities to fully develop their capabilities. It examines the relevance and limitations of a social norms lens for both understanding and overcoming constraints on girls' capability development. The chapter highlights the potential of integrating a greater understanding of power relations and empowerment, and situating norm change activities within a fuller consideration of the broader institutional environment. It also outlines an analytical approach related to norms, agency, power and capability development that the authors believe points to a productive way of understanding the constraints that limit adolescent girls' development and ways of overcoming them.