This chapter describes the development, scope, and application of international environmental law, which has expanded significantly since the late 1960s. The focus is on international treaties relating to environmental protection. The chapter is restricted to discussing public, rather than private, international law—that is, the law between states, rather than the conflict of legal systems. International law has often been regarded as something rather closer to international relations due to the fact that there is no single body with the power to make and enforce law against states, companies, or individuals effectively. In the UK, international law does not necessarily have a direct impact on domestic law or on individuals. Treaties need to be given effect to through national legislation and are concerned with the action of states, not individuals within states—with some notable exceptions, such as the law on war crimes.