Two trends are emerging in International Relations (IR). One is the increasing receptiveness of scholars to insights from behavioural economics; the other is their growing interest in the role of emotions. These two trends have one thing in common: they both seek to bust the myth of rationality. Admittedly, many IR theories have already attempted to do so (e.g. constructivism, post-structuralism, feminism, or practice theory). However, these new approaches differ from the old ones in one important respect: they are more empirical because they are grounded in experimental and neuroscientific findings. This creates an opportunity for an interesting new body of IR scholarship. Before I get to that, let me first say a few words about behavioral economics and the scholarly turn towards emotions.