This chapter presents the broader theoretical framework informing the book—social constructivism or, simply, constructivism—paving the way for the study of the influence of ideational aspects (the concept of peacebuilding) in world politics (UN support to societies emerging from conflict). It offers an account of the origins of constructivism in the field of International Relations (IR) and delves into a discussion of what constructivism generally is all about: a set of social theory tenets that provide helpful insights for the study of social relations in general and world politics in particular. Finally, the chapter elaborates on how social science theories may influence political outcomes in world politics and outlines the research framework that allows for a discussion on how the concept of peacebuilding gained life and its implications for the United Nations approach to societies affected by armed conflict.