Types of International Law: How Are They Different and Why?

By Linda C. Ashar, J.D.  |  11/03/2025

Global businesses today operate within a legal landscape that involves cross-border transactions, conflicting economic interests, and complex international relations. Similarly, the modern international law environment incorporates many substantive rules and international laws that form a global legal system. This legal landscape includes areas such as treaty law, customary international law, and international court decisions designed to help maintain international peace.

International organizations and regional organizations play a key role in shaping international cooperation and diplomatic relations among sovereign states and other national entities. These organizations include:

• The United Nations (UN)
• The World Trade Organization (WTO)
• The Association of Southeast Asian Nations (ASEAN)

The international community relies on international organizations such as the International Court of Justice (ICJ) (also called the World Court) for peaceful settlement of civil disputes. For international criminal law, the International Criminal Court (ICC) metes out international criminal justice, including war crimes and violations of humanitarian law.

International law now directly shapes industry, especially how private companies trade, innovate, and compete. However, the legislation governing commerce is evolving rapidly. As a result, legal compliance has become both a strategic necessity and a reputational imperative.

International business must also be aware of how domestic law and municipal law intersect with international rules and agreements, especially in areas such as:

• Digital privacy compliance
• Crisis management
• International environmental law
• International human rights law

Types of International Law

Understanding different types of international law is essential for businesses to successfully navigate the risks and opportunities in a globalized economy. These types of laws include:

• Public international law
• Customary international law
• Supranational law
• Private international law

Public International Law

Public international law governs the relationships between sovereign states and intergovernmental organizations like the United Nations (UN). It includes treaties such as the Kyoto Protocol and the Paris Agreement and the rules of customary practice between sovereign states.

For business, this category of international law affects provisions of international agreements and trade. It also impacts environmental obligations and dispute settlements.

For the enforcement and recognition of international agreements, international affairs often require engagement with:

• International actors
• National courts
• Permanent international courts

A notable example of the Paris Agreement’s effect on business decision-making is the automotive industry’s shift toward electric vehicles (EVs). In response to national commitments under the Paris Agreement to reduce greenhouse gas emissions, major car manufacturers like Volkswagen have committed to phasing out internal combustion engine production. Instead, the production of EVs will likely increase over the next decade, driven largely by the European market’s shift toward carbon-neutral goals.

Similarly, businesses will be challenged by broader regulatory schemes to create innovative solutions and meet international demands for environmental change.

It is not only the European Union (EU) forcing change, however. Another prominent example is India, which is drawing international global business attention for growth and investment.

Following the Paris Agreement, India set national ambitious targets that directly influence business strategies. India now requires companies across all sectors to improve their energy efficiency and adopt cleaner processes.

Researchers Yisha Nadav and Fincy Palissery noted that pursuant to the Government of India’s push for progress toward net-zero carbon emissions, environmental protection is a “key non-negotiable” provision in India’s international investment agreements. This legal compliance measure has affected businesses who desire to operate or invest in India.

Customary International Law

Customary international law refers what Article 38 of the International Court of Justice describes as “a general practice accepted as law,” such as prohibitions against forced labor or expectations of environmental stewardship.

Customary international law is not a codified volume of law. Similar to common law, customary international law is the long-standing general practice of principles and standards accepted as legally binding (opinio juris) by the international community, even above individual treaties. An example is the diplomatic immunity accorded by visiting heads of state and their official ambassadors.

Humanitarian law principles significantly took center stage in the international law arena following World War II. The issues spotlighted in the Nuremberg trials and provisions of the Geneva Conventions were expanded beyond their defined boundaries to occupy the broader realm of customary international law.

As the UN’s Office of the High Commissioner for Human Rights explains, “Many of the provisions contained in the Geneva Conventions and their Protocols are considered to be part of customary international law and applicable in any armed conflict.”

Customary international law refers to widely recognized norms that encompass:

• Prohibitions against forced labor
• Terrorism
• Expectations of environmental stewardship

Increasingly, multinational corporations are held to these standards through stakeholder expectations of supply chain due diligence, responsible human rights practices, and corporate sustainability practices.

Supranational Law

Supranational law (also known as regional law) is a legal framework created when sovereign states transfer parts of their sovereignty to a common supranational organization. This practice establishes a higher authority that can issue laws and make decisions with direct effect within member states.

The European Union is a prominent example of a supranational organization whose laws have supremacy over national court decisions on matters covered by EU law. This type of law differs from traditional international law because member states transfer their right to make certain judicial decisions to institutions such as the Court of Justice of the European Union (CJEU).  

Another example of supranational law is the United States-Mexico-Canada-Agreement (USMCA), a three-way trade agreement. USMCA governs certain aspects of economic and trade matters, such as:

• Digital trade
• Intellectual property
• Labor and environmental standards
• Agriculture
• The automotive industry

Supranational law includes provisions like EU directives, the USMCA, and the activities of international alliances like ASEAN, that can override or supplement domestic law. As a result, companies must adjust their operations, which may interject uncertainty into local operations.

For example, the implementation of the General Data Protection Regulation (GDPR) in the European Union has required global companies to overhaul how they collect, process, and store personal data. As a result, U.S.-based tech firms with European customers have had to appoint EU data protection representatives and update their privacy policies. Otherwise, these tech firms would face hefty fines for non-compliance.

A court of supranational law jurisdiction is the European Court of Human Rights (ECtHR), which adjudicates claims alleging violations of civil and political rights under the European Convention of Human Rights (ECHR). This court is a forum for international disputes where member states, individuals, and corporations can petition for redress.

UK legal advisors Emilie Jones and David Thorneloe explain that businesses possess at least four key ECHR rights against a violation from another member of the EHCR. The rights include:

• The right to property
• The right to freedom of expression
• The right to a fair hearing
• The right to privacy 

There are currently 46 member nations in the ECHR. Some ECHR member nations, like the UK, have further codified these rights in national legislation.

Private International Law

Private international law addresses the question of which nation’s laws, procedures, and legal framework should govern a dispute when it spans more than one jurisdiction. Because differences in laws among countries occur at times, this source of international law is concerned about which jurisdiction’s rules should apply (a conflict of laws) in international cross-border contract disputes or other disputes.

For example, when a U.S. company sells software to a European firm, the enforceability of the contract and recognition of a court judgment for enforcement fall under this category. Increased commerce in cross-border transactions and the increase in speed and types of transactions has made legal questions more complex.

Specific laws create overlapping and potentially conflicting private corporate legal obligations. These laws include:

• China’s Personal Informational Protection Law (PIPL)
• Brazil’s General Personal Data Protection Act (LGPD)
• U.S. state-level laws such as Illinois’ Biometric Information Privacy Act (BIPA)

Complying with “nation A’s” law might conflict with the ability for a business to conduct operations in its home country or with its plans to expand in “nation B.”

Private international law can also create reputational risk through a lack of knowledge or understanding of a nation's laws. For instance, both McDonald’s® and Coca-Cola® experienced a sensational debacle over their commercial use of Saudi Arabia’s flag in their 1994 World Cup marketing materials. This illegal use of a flag for a sports event created a foreign relations incident for these companies.

Countries are busy innovating and expanding laws that might seem similar to other nations but contain legal trapdoors. Emerging governance of artificial intelligence further complicates business compliance risk.

The EU has implemented aggressive artificial intelligence (AI) regulations, while federal U.S. law has not. However, some individual states have implemented AI controls.

Individual national laws also have global reach against corporations. An example is the U.S. Foreign Corrupt Practices Act (FCPA), which prohibits bribery. It applies to U.S. companies and foreign companies listed on U.S. stock exchanges.

The Future of International Law

Today, international law is neither abstract nor an optional consideration for business. However, the challenge for businesses now is to not only comply with various laws but integrate their obligations and practical good sense into sound strategy.

As international legal systems continue to evolve, businesses are challenged to remain informed. They will need to keep up with:

• International law developments
• Court decisions
• Environmental agreements
• The activities of newly independent states seeking commercial trade and infrastructure partnerships

In the future, AI governance, environmental obligations, and digital trade regulation will intensify. Companies with the foresight to invest in governance, compliance, and ethical practices will mitigate their risks and gain a competitive advantage.

The Bachelor of Legal Studies at APU

For adult learners interested in gaining a knowledge of different types of law, the U.S. court system, and other legal topics, American Public University (APU) offers an online Bachelor of Science in Legal Studies. In this legal studies degree program, students can take courses in civil practice and procedures, constitutional law, and civil practice and procedures.

This B.S. in Legal Studies also has eight concentrations so that students can choose the courses that suit their professional interests. Students interested in international law may opt for the General concentration, which offers a course in international law and related topics.

For more information, visit APU’s security and global studies degree program page.

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Note: Completion of this program does not award any professional paralegal or any other certification but may be helpful in preparing to seek such certifications.