The problems of pollution are not limited to the borders of any one country. Because the harmful effects of pollution often extend to areas beyond the country where the pollution originated, the international legal system is an important means of controlling pollution. (The text here refers to "countries," but the reader should be aware that countries are usually termed "states" in the parlance of international law.) International efforts to control pollution are numerous and complex. The following section identifies some of the main features of the system.

International Legal System

The two primary sources of international law are custom and treaties, and both play a role in regulating international pollution. Customary international law emerges when countries engage in certain practices in the belief that those practices are required by international law. To become customary law, a practice must be generally followed, rather...