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International Law and Municipal Law: Application & Relationship 2024

With regard to the question of the relationship between International Law and municipal law, the theoretical question is whether International Law and municipal law are part of a single legal order or they are comprised of two distinct systems of law.

The question above raises further questions, namely;

the status of rules of municipal law before international tribunals

The circumstances in which rules of Public International Law will be applied by a municipal court, and

What happens if a rule of municipal law is in conflict with a rule of International Law?

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Here you will find answers to those questions, including

  • What is municipal law
  • what is an international law
  • Relationships between International Law and Municipal Law
  • Application of Municipal Law in International Courts and Tribunals
  • etc

let’s get started

Municipal law

Municipal law is the body of legislation that applies specifically to a given city, county, or other government entity (referred to in legalese as a “municipality”).

This can apply to a variety of topics, such as property taxes, zoning regulations, police power, and educational programs.

The majority of municipalities themselves engage attorneys to manage their legal matters. The lawyers may even serve as corporate counsel for the cities, meaning that they only represent that specific city.

Municipal legislation is primarily drafted by local city or town governments. Local residents have a lot of influence over municipal law, which can differ greatly between municipalities because council members are chosen by the town’s citizens.

If you think you may have a municipal law issue, make sure to speak with a lawyer who is familiar with the local ordinances.

International law

International law is a body of treaties and agreements between countries that regulates how they deal with other countries, their residents, and their businesses. 

International law often divides into two groups. Conflicts involving private parties, such as individuals or corporations, who have a close connection to multiple countries are the subject of “private international law.”

For instance, claims resulting from the Union Carbide-owned industrial plants that leaked deadly gas in Bhopal, India, would be regarded as a subject of private international law.

The subject of “public international law” is interstate interactions.

These cover norms of conduct on a global scale, maritime laws, economic and diplomatic rules, laws protecting the environment, laws protecting human rights, and laws governing humanitarian aid.

A number of accords have “codified” some concepts of public international law, but others have not been codified anywhere. These laws are referred to be “customary,” and nations accept them by doing nothing.

The enforcement of international law is typically left to the individual states because most of it is established by treaties.

Certain international institutions do, however, enforce certain treaties.

The United Nations, which has 192 member states, is the most noteworthy example.

Read also: Main sources of Public International law

The Relationship between International Law and Municipal Law

The Relationship between International Law and Municipal Law

There are two doctrines that have sought to clarify the relationship between International Law and Municipal Law.

These doctrines are referred to as monism and dualism.

Monism entails that, international law and municipal law are both parts of a single legal structure while dualism presupposes that international law and municipal law are separate systems.


Monism is an international law doctrine that explains the relationship between municipal law and international law.

This doctrine holds that International Law and municipal law are both parts of a single legal structure. 

Thus the monist considers municipal law and international law to operate within a common field and to be concerned with the same subject matter.

With monism, if there is a conflict between municipal law and international law, then the rules of International Law shall prevail.

Further, in the monist practice, once a treaty is, signed it becomes part of the law of the land immediately and automatically.


Dualism is also an international law doctrine that explains the relationship between municipal law and international law.

The dualists argue that International Law and municipal law are separate systems whereby international law regulates relations between states, while municipal law regulates relations between the state and its citizens.

With Dualism International Law operates in the municipal sphere only when there is a specific act to adopt the law and in case of conflict between the two, municipal law can give effect to International Law.

Application of Municipal Law in International Courts and Tribunals

It is well settled in international law that the judgments of a national court may constitute a source of International Law.

While this is the case, the general rule is that the state may not rely upon a provision of municipal law as an excuse for a breach of international obligations.

Article 27 of the Vienna Convention on the Law of Treaties (1969) provides that, a party may not involve the provisions of its internal law as justification for its failure to perform a treaty. Therefore, obligations arising under International Law prevail over municipal law.

Therefore states must ensure that their domestic legislation is in line with international obligations.

Application of International Law in Municipal Courts

The status and treatment of International Law in municipal courts differs from state to state. 

The starting point is the constitutional arrangement of a particular state regarding the application of international law in their state.

In the legal system of a country, it is usually stated how International Law is to be treated by the courts of that state.

For example, the US The Constitution of the United States stipulates (Article VI, Section 2) that treaties “shall be the supreme Law of the Land.” Treaties are negotiated by the president but can be ratified only with the approval of two-thirds of the Senate (Article II)—except in the case of executive agreements, which are made by the president under his own authority.

Generally, there are two doctrines that explain the application of international law in municipal courts i.e. the doctrine of incorporation and the doctrine of transformation.

The Doctrine of Incorporation

The doctrine of incorporation holds that International Law is automatically part of municipal law, without any express act of adoption.

In such a situation, a treaty signed and ratified by a state would become binding on the citizen of that state, without any legislation being passed. 

As such in some states, the constitution of the state will provide that rules of International Law should become automatically part of municipal law.

In principle, The doctrine of Incorporation follows the monist approach.

Doctrine of Transformation

The doctrine of transformation holds that the rules of International Law do not become part of municipal law, unless and until there has been an express act of adoption.

Therefore, a rule of International Law must be transformed into domestic law.

Thus, if a state has entered into a treaty, that instrument would not be given effect in the courts of the state, unless domestic legislation had been enacted to transform it into municipal law.

The Doctrine of Transformation follows the dualist approach.


Isack Kimaro
Isack Kimaro

Isack Kimaro, a lawyer, Creative Writer and self-taught SEO expert has been a prominent author of law-related topics since 2017. Through hard work, dedication, and a relentless pursuit of knowledge, Isack has successfully navigated the legal industry by providing valuable and easy-to-understand legal information to 500,000+ individuals of all levels of understanding.