Interest in international law has increased greatly over the past decade, largely because of its central place in discussions such as the Iraq War and Guantanamo, the World Trade Organisation, the anti-capitalist movement, the Kyoto Convention on climate change, and the apparent failure of the international system to deal with the situations in Palestine and Darfur, and the plights of refugees and illegal immigrants around the world. This Very Short Introduction explains what international law is, what its role in international society is, and how it operates. Vaughan Lowe examines what international law can and cannot do and what it is and what it isn't doing to make the world a better place. Focussing on the problems the world faces, Lowe uses terrorism, environmental change, poverty, and international violence to demonstrate the theories and practice of international law, and how the principles can be used for international co-operation.