The discipline of IR is beginning to grapple with how nature is a condition for, and increasingly and object of, international politics. This chapter narrates how IR actually began with features of the natural world at its heart, narrowed this down to human nature, before then losing sight of it almost entirely – only to rediscover it years later as ‘the environment’. A recent revival of realist geopolitics brings geography back in, but misses the environmental angle as well as the Anthropocene idea that due to human influence nature is now more dynamic, more prone to harm and in some ways more threatening than before. To theorise a non-anthropocentric IR, one way forward is to develop concepts that integrate the human with the non-human, as some post-human and ‘new materialist’ approaches do. Another strategy is to maintain an analytical distinction between the social and the natural, but then to think in dialectical terms about their mutual relations and transformations. Neither strategy is without pitfalls, but I suggest that the latter deserves more attention.