These days it seems like everyone knows about ‘black swans.’ Natalie Portman and Mila Kunis aside, Nassim Nicholas Taleb used it as the title for his 2007 book about “low probability, high impact” events to which, he argued, the human mind is especially vulnerable. But ‘black swans’ have an older role in debates about the philosophy of science (as Taleb, a self-described epistemologist, certainly knew) and, thus, relevance for International Relations, a discipline that often aspires to (social) scientific status.