For IR, the contribution of green theory helps us re-examine the relationship between the state, the economy and the environment. IR normally sets this in the context of globalisation viewed from the limited perspective of states and markets – but globalisation also involves opportunities for developing shared global ecological values. Green theory has the potential to radically challenge the idea of sovereign nation states operating in competition and is thus part of the post-Westphalian trend in IR thought. Of course, the greater contribution of green theory, or its capacity for critical engagement with IR, lies in its very different origins – taking planetary ecology as a starting point and looking beyond our current political-economic structures. Green theory is thus able to offer not just an alternative description of our world but also a different logic for understanding it – and how we might act to change it. IR theory is likely to be disrupted and re-oriented by green theory, not so much because greens will win the arguments but because IR theorists will inevitably have to provide a coherent account of how we all live sustainably on our planet. This means that at some point we may have to stop theorising about the state-centric ‘inter-national’ and find another political point of reference in human relationships, such as policy networks or social movements.