This chapter examines the contribution made by the “emotional turn,” one of the most exciting and revolutionary developments in contemporary scholarship, to the key concerns of contemporary International Political Theory (IPT). It details the particularly close relationship that has been forged between empirical research on the emotions and IPT, and examines the role that discoveries in the neurosciences and psychology may play in substantiating existing emotional theories of international relations and shaping new developments in international political thought. The chapter also considers the broader implications of emotions research for IPT, focusing in particular on the impact that key findings about the nature of reason and its relationship to the emotions may have on the core assumptions that underpin many dominant theoretical accounts of international relations.