This chapter will examine the key debates that have shaped the development of constructivism in International Relations (IR). The introduction and first section will explore the general notion that international relations is a social construction, as it emerged from the critique of more traditional theories of IR. The second and third sections will examine the demarcations that have distinguish various constructivisms, focusing in particular on the contrast between to those who seek a better social science, and therefore better theory, as opposed to those who argue that constructivism is an approach that rests on assumptions at odds with those of positivist method. The fourth section will analyse the significance of this difference for undertak ing research, including questions about the role of language and causality. The final section will bring these insights to bear in relation to the War on Terror