International criminal law is a subdivision of public international law which concentrates on the punishment of the individuals who committed acts defined by international law as crimes. The notion of international crimes has a broad interpretation, nevertheless, it usually concerns genocides, crimes against humanity, war crimes, and the crimes of aggression. Issues of piracy, terrorism, slavery, drug trafficking are not treated as international crimes.
The sources of international criminal law include international conventions and treaties, international customary law, general principles of law, judicial decisions, and learned writings. The relevance of these sources differs from one country to another which means various countries may apply these sources in different ways.
Among treaty sources of international criminal law, the Genocide Convention and the grave breaches provisions of the four 1949 Geneva Conventions. However, numerous other treaties which are not as widely ratified as the Geneva Conventions are also included to the sources of international criminal law.
Customs are consistent, uniform, and general state practices. While treaties bind only their parties, general customary law binds all states. However, it is usually more difficult to define the content of the custom law precisely which makes treaty law more preferable. Diplomatic correspondence, official policy statements, governmental press releases and many other documents may serve to define state’s practices.
Principles of law are formulated by examining the national laws and international legal practices. These principles are generally accepted as a fundamental rule of justice by most nations which makes them a valid source of international criminal law.
In the exceptional situations, the appeals chamber may be guided by its prior judicial decisions. Trial chambers, in their turn, must follow the decisions of the appeals chamber.