How is International Law Created?

Unlike with the domestic laws of individual countries, there is no single international government that creates and enforces international law. Consequently, international law has developed as a result of countries agreeing to act or refrain from acting in certain ways toward one another. There are two main ways that international laws are developed: through the adoption of customs and the signing of treaties.

Customary International Law

Usually when we think about customs, we think about the established habits or behaviours of a community that have developed and become accepted as rules. The international community also has certain customs that have developed and been followed over long periods of time. These customs become international customary law after countries repeatedly behave in a particular way because their leaders believe they are required to do so. Whether or not countries are actually required by a formal law to act that way doesn’t matter, so long as countries believe they must act a particular way and continue to do so over a period of time. Customary law is based on what countries actually do, rather than what they have formally agreed to do – as we shall see, this is how customary international law differs from the signing of treaties.

When enough countries engage in a particular behaviour for long enough, that behaviour will become part of customary international law. For example, the law of diplomatic immunity - which protects diplomats from harm or lawsuits when in a foreign country - began as a custom. There are no rules that set out how many countries must participate in the behaviour or for how long. If certain behaviours become a part of customary international law then they will be legally binding on all countries.

The strength of customary international law is that all countries can be bound to follow it even if they don’t expressly agree to follow a particular behaviour. The weaknesses are that it is slow to change because it is based on continued behaviour over time and often the laws that result from customary behaviour are unclear and imprecise because of the way they developed. Because these laws may be imprecise, they can cause disputes between countries over what is actually part of the law.


The term ‘treaty’ refers to a formal agreement between two or more states that sets out their mutual legal rights and obligations. Treaties are often made with regard to peace, the creation of alliances, commerce and trade, and other international relations. Interestingly, formal agreements between First Nations in Canada and the Crown are termed “treaties.” International treaties may establish general rules of law, such as the protection of human rights, or provide for contract-like obligations between countries, such as treaties dealing with international trade. Treaties may be very specific or quite broad, making them versatile for the creation of law.


For a state to be bound by a treaty, the state must ratify, or officially consent to be bound by that treaty. Signing a treaty is not the same thing as ratifying a treaty. Treaties may be bilateral, meaning that an agreement is formed between two countries, or multilateral, meaning that the agreement is between three or more countries. A multilateral treaty may even include most of the countries in the world.

The advantages of treaties are that they can be created quickly and contain a clear explanation of the law being created. Treaties may also influence the behaviour of countries toward one another and end up affecting other types of international law, such as customary international law. A disadvantage of treaties is that they only bind those countries that agree to be part of the treaty.

International treaties go by many names. Some of these include:

  • Conventions
  • Charters
  • Covenants
  • Protocols
  • Pacts
  • Acts
  • Statutes
  • Agreements

Although treaties and custom are the main sources for international law, several other sources exist that can be important for lawyers arguing a case on international law. These sources are the decisions of other courts on matters of international law (jurisprudence), the writings of scholars and academics on international law matters and general legal principles, such as the rule of law.