In previous chapters we referred to sustainable development as a principle of global concern. However, we have not yet explored how problems of unsustainable development which have an international dimension can be addressed. So far we have treated environmental problems and policies as if the generators and victims of unsustainable economic activities resided within a single country. This allowed us to focus on the governance mechanisms which induce or enforce more sustainable production and consumption choices. These mechanisms can operate because the primacy given to the nation state in political affairs provides the legitimacy and authority needed to support them. However, many important environmental problems concern effects on individuals who live (or are yet to live) in different nation states. Humankind faces an unprecedented array of truly global and regional environmental problems, the reach of which is greater than any single national community (or generation). Chapter 12 sets out some basic ideas and information about trade between states in relation to sustainable development. Then, in Chapters 13 and 14, we look at two global threats to sustainability: climate change and biodiversity loss.