Principles of International Law

International humanitarian law (IHL) is part of international law. Therefore, basic knowledge of international law is necessary for the understanding of IHL. International law is a combination of rules and customs governing the relations between states in different fields, such as the law of the sea, space law, trade law, territorial boundaries of states, and diplomatic relations.

Sources of International Law

The sources of international law are treaty law and international customary law.

Treaty law

Treaty law is composed of treaties, which are agreements that states willingly sign and ratify and are obliged to follow. Agreements between states govern the mutual relations between them and may be called conventions, statutes
or protocols. Agreements are only legally binding on states that signed and also ratified them. The basis of Treaty law is the rule of law ‘pacta sunt servanda’, which means, that agreements must be honoured, and adhered to.

International customary law

Unlike treaty law, which must be followed only by states that are parties to the agreement in question, international customary law is binding upon all states, no matter whether they have ratified a treaty, which contain the rule in question, or not.

How does a rule become customary international law?

When states act consistently in their international and internal relations during a long period of time, these actions/practises become accepted by the international community as applicable law.

International customary law is compromised of all the written or unwritten rules that form part of the general international idea of justice.

Two criterias

There are two criterias for identifying a rule as part of international customary law.

Opinio Juris - Opino Juris is the expressed opinion of states that their actions have a legal basis. It is thus states themselves (subjective criteria) that recognise certain legal practices or rules as being legally binding.

Usus - Customary law is confirmed through the actions of states (objective criteria) in accordance with what is expected of them by international jurisprudence. States' actions are manifested through their official statements and actual actions.

International customary law is based on prolonged and consistent actions by most states in the world. When states act constintently in their international and internal relations during a long period of time these actions/practices become accepted by the international community as applicable law.

Examples of international customary law are the right to life, the prohibition of torture, and that civilians should not be the object of an attack.

Jus cogens

A number of rules of international law are part of the Latin concept of "jus cogens", also referred to as peremptory norms, and meaning "the compelling law". Jus cogens status is the highest status that can be attained by any principles or norms in international law.

Jus cogens status is given only to the most fundamental rules of international law, which are recognised and accepted by the international community as rules from which no exceptions can be made (article 53 of the Vienna Convention on the Law of Treaties).

All states are obliged to follow jus cogens rules at all times. Crimes which have attained the status of jus cogens are particularly outrageous crimes, which are seen as affecting the international community as a whole, such as genocide, slavery and torture.

To the Vienna Convention on the Law of Treaties

Erga omnes

A number of particularly heinous crimes - normally those that are categorised as violations of jus cogens rules - give rise to so called "erga omnes" obligations. Erga omnes is another Latin concept and means "towards all".

Just as the jus cogens crimes, the crimes that give rise to erga omnes obligations are seen as affecting the international community as a whole, and consequently all states in the world have an obligation to take action against the perpetrators of such crimes.

For example, states should search for and prosecute the perpetrators. This obligation follows from what is called
the principle of universal jurisdiction - all national courts in the world can put perpetrators of erga omnes crimes to trial.

Both states and individuals can be held responsible for erga omnes crimes.

Read more about individual criminal responsibility