A body of law, governing the acceptable action of global society, international criminal law is derived from a number of areas including general principles of international law recognized by civilized nations, the general criminal law recognized by nations within national boundaries, and the treaties which govern particular conduct between and among nations. Rules and principles of international law are not technically enforceable since there is no actual world government. Rather, international laws have been considered obligatory standards of behavior. Lack of total enforcement and an occasional violation are not regarded as negating any aspect of International Law. Likewise, it is no defense for a nation to point out that its own law or constitution permits actions that other nations consider a violation of international law.

In ancient and medieval times, international relations were regulated by special treaties between rulers. Among the city-states of ancient Greece there were a few principles of international procedure, such as the protection of ambassadors, but there was no body of recognized law. The medieval Italians were the first to work out a code comparable to modern international law. A few rulers developed a system of passports, established the distinction between armies and civilians in war, and set rules for warfare.

International criminal law can be defined as international (an offense against the global community) or transnational (an offense against one or several nations). Crimes in the international category would include acts which threaten world order and security, crimes against humanity (also known as human rights violations), war crimes, and genocide. Transnational crime would encompass actions such as drug trafficking, organized criminal activity taking place across borders, counterfeiting, money laundering, financial crimes, terrorism, and willful damage to the environment.

Many issues encompassed within the discipline of international criminal law are addressed by some type of agreement or convention, often overseen by an intergovernmental organization, such as the United Nations (UN). Major UN treaties and conventions include the UN Charter and conventions on apartheid, genocide, war crimes and crimes against humanity, torture, narcotic drugs, slavery, the taking of hostages, aircraft hijacking, and terrorism.

A nation, to be recognized as such by other nations, must be independent of foreign control and must be willing to live according to international law. A nation possesses supreme authority, or sovereignty (called jurisdiction), over all territory, objects, and persons within its borders. It may also exercise jurisdiction over its own property and its nationals and their property in foreign jurisdictions, subject to the jurisdiction of other nations as set forth in international law or treaties. Exempt from the local jurisdiction of any nation are foreign nations as such, their officials, chiefs of state, diplomatic and consular representatives, military personnel, and their property. One nation may not be sued in the courts of a second, nor may legal action be taken against its officials or its property. Formal, or de jure, recognition of a nation is irrevocable. It continues in effect notwithstanding changes of territory, population, and social or political organization, unless the changes destroy the identity of the nation.

After the middle of the nineteenth century, several nations set down existing law in written systematic form, called codification. This work was carried forward in the 1930s by the League of Nations and passed in 1945 to the United Nations (UN). The UN Charter states that one of the organization's main purposes is the settlement of international disputes. To carry out the human rights provisions of the charter, the General Assembly set up a commission to draft an international Covenant of Human Rights. In 1948 the Assembly adopted a Convention on Genocide, which makes the destruction of a people an international crime. The trials of war criminals in Germany and Japan extended international criminal law to individuals. In 1947 the General Assembly created the International Law Commission as an auxiliary, but autonomous, body. The commission consists of 25 members with recognized competence in international law.

The International Court of Justice is the principal judicial organ of the United Nations. Its seat is at the Peace Palace in The Hague, which is located in the Netherlands. It was founded in 1946, when it replaced the Permanent Court of International Justice, which had functioned in the Peace Palace since 1922. It operates under a Statute largely similar to that of its predecessor, which is an integral part of the Charter of the United Nations. The Court's mission is to resolve the legal disputes submitted to it by States, and to give advisory opinions on legal questions referred to it by duly authorized international agencies.

The Court is composed of fifteen judges elected to nine-year terms of office by the United Nations General Assembly and Security Council sitting independently of each other. It may not include more than one judge of any nationality. Elections are held every three years for one-third of the seats. Retiring judges may be re-elected. The Members of the Court do not represent their governments but are independent magistrates. When the Court does not include a judge possessing the nationality of a State party to a case, that State may appoint a person to sit as a judge ad hoc for the purpose of the case. Only States may apply to and appear before the Court. The States which are Members of the United Nations and one State which is not a Member of the United Nations but which has become party to the Court's Statute (Switzerland) are allowed to bring cases before the court. As of 2000, the advisory procedure of the Court was open solely to international organizations. The only bodies authorized to request advisory opinions of the Court are five organs of the United Nations itself and the specialized agencies of the United Nations family.

Under international legal principles, war may not be started without declaration to the enemy and notice to neutrals, though acts permissible only in a state of war, such as a blockade, bring war into existence even in absence of a declaration. In war, troops must be placed under effective control of national officers and must be designated by uniforms, flags, or other distinctive marks. Neither poison nor explosive bullets nor any weapon that causes unnecessary suffering are supposed to be used. Religious, philanthropic, educational, artistic, or scientific property of the enemy is exempt from seizure or injury, as well as medical establishments connected with fighting forces. Similarly a mission bearing a white flag or other sign of surrender is not supposed to be attacked. Enemy combatants may be captured or rendered incapable of further action by armed forces when encountered in national or enemy territory. But civilians are not supposed to be harmed unless they use force. At the outbreak of war, enemy aliens may be expelled from the national territory, interned, or deprived of civil rights. A person captured under suspicion of being an enemy spy must be given a military trial and can be punished by death if found guilty.

International law outlines what can be done with prisoners of war. They are not supposed to be imprisoned beyond what is necessary for safety or discipline and cannot be forced to render military service, though they may be compelled to render other services, supposedly at rates of pay prevailing in the locality. Sick and injured prisoners are supposed to be provided adequate medical care. The dead are supposed to be identified and then buried or cremated, with lists of prisoners and dead given to the enemy.

International Criminal Law. World of Criminal Justice, Gale (2002).