The Introduction identifies a tradition of critical scholarship in International Relations (IR) according to which truth and knowledge are to be seen as social and political phenomena which play a key role in constituting international realities. There has already been extensive reflection on epistemic matters in IR, and many theorists now believe it is time to move on. However, wider societal concerns about truth, the interventions of Critical Realists, and the relative neglect of the work of early Critical Theorists suggest that there is much more to be said on this topic and about the ways it has been tackled in the discipline.