33.2 Sources and Practice of International Law

Learning Objectives

  1. Explain what a treaty is and how it differs from a convention.
  2. Understand that a treaty can be a voluntary relinquishment of some aspects of sovereignty.
  3. Describe customary international law, and explain how it is different from treaties as a source of international law.
  4. Describe some of the difficulties in enforcing one nation’s judicial judgments in another nation.

In this section, we shall be looking at a number of different sources of international law. These sources include treaties and conventions, decisions of courts in various countries (including decisions in your own state and nation), decisions of regional courts (such as the European Court of Justice), the World Trade Organization (WTO), resolutions of the United Nations (UN), and decisions by regional trade organizations such as the North American Free Trade Agreement (NAFTA). These sources are different from most of the cases in your textbook, either because they involve parties from different nations or because the rule makers or decision makers affect entities beyond their own borders.

In brief, the sources of international law include everything that an international tribunal might rely on to decide international disputes. International disputes include arguments between nations, arguments between individuals or companies from different nations, and disputes between individuals or companies and a foreign nation-state. Article 38(1) of the Statute of the International Court of Justice (ICJ) lists four sources of international law: treaties and conventions, custom, general principles of law, and judicial decisions and teachings.

The ICJ only hears lawsuits between nation-states. Its jurisdiction is not compulsory, meaning that both nations in a dispute must agree to have the ICJ hear the dispute.

Treaties and Conventions

Even after signing a treaty or convention, a nation is always free to go it alone and repudiate all regional or international bodies, or refuse to obey the dictates of the United Nations or, more broadly and ambiguously, “the community of nations.” The United States could repudiate NAFTA, could withdraw from the UN, and could let the WTO know that it would no longer abide by the post–World War II rules of free trade embodied in the General Agreement on Tariffs and Trade (GATT). The United States would be within its rights as a sovereign to do so, since it owes allegiance to no global or international sovereign. Why, however, does it not do so? Why is the United States so involved with the “entangling alliances” that George Washington warned about? Simply put, nations will give away part of their sovereignty if they think it’s in their self-interest to do so. For example, if Latvia joins the European Union (EU), it gives up its right to have its own currency but believes it has more to gain.

A treatyAn agreement between two or more nation-states. In US law, a treaty has the same standing as a federal statute. is nothing more than an agreement between two sovereign nations. In international law, a nation is usually called a state or nation-stateUnder international law, the common term for a country or a nation.. This can be confusing, since there are fifty US states, none of which has power to make treaties with other countries. It may be helpful to recall that the thirteen original states under the Articles of Confederation were in fact able to have direct relations with foreign states. Thus New Jersey (for a few brief years) could have had an ambassador to France or made treaties with Spain. Such a decentralized confederation did not last long. Under the present Constitution, states gave up their right to deal directly with other countries and vested that power in the federal government.

There are many treaties to which the United States is a party. Some of these are conventionsMultilateral treaties that are sponsored by an international agency or institution (e.g., the United Nations)., which are treaties on matters of common concern, usually negotiated on a regional or global basis, sponsored by an international organization, and open to adoption by many nations. For example, as of 2011, there were 192 parties (nation-states) that had signed on to the Charter of the UN, including the United States, Uzbekistan, Ukraine, Uganda, United Arab Emirates, United Kingdom of Great Britain and Northern Ireland, and Uruguay (just to name a few of the nations starting with U).

The most basic kind of treaty is an agreement between two nation-states on matters of trade and friendly relations. Treaties of friendship, commerce, and navigation (FCN treaties) are fairly common and provide for mutual respect for each nation-state’s citizens in (1) rights of entry, (2) practice of professions, (3) right of navigation, (4) acquisition of property, (5) matters of expropriation or nationalization, (6) access to courts, and (7) protection of patent rights. Bilateral investment treaties (BITs) are similar but are more focused on commerce and investment. The commercial treaties may deal with a specific product or product group, investment, tariffs, or taxation.

Nation-states customarily enter not only into FCN treaties and BITs but also into peace treaties or weapons limitations treaties, such as the US-Russia Strategic Arms Reduction Talks (START) treaty. Again, treaties are only binding as long as each party continues to recognize their binding effect. In the United States, the procedure for ratifying a treaty is that the Senate must approve it by a two-thirds vote (politically, an especially difficult number to achieve). Once ratified, a treaty has the same force of law within the United States as any statute that Congress might pass.


Custom between nations is another source of international law. Custom is practice followed by two or more nations in the course of dealing with each other. These practices can be found in diplomatic correspondence, policy statements, or official government statements. To become custom, a consistent and recurring practice must go on over a significant period of time, and nations must recognize that the practice or custom is binding and must follow it because of legal obligation and not mere courtesy. Customs may become codified in treaties.

General Principles of Law, or Customary International Law

Even without treaties, there would be some international law, since not all disputes are confined to the territory of one nation-state. For example, in In re the Bremen, a US company’s disagreement with a German company was heard in US courts. The US courts had to decide where the dispute would properly be heard. In giving full effect to a forum-selection clause, the US Supreme Court set out a principle that it hoped would be honored by courts of other nations—namely, that companies from different states should honor any forum-selection clauseIn a contract, national or international, the parties may specify the court where any disputes between the parties will be settled. See the Bremen case. in their contract to settle disputes at a specific place or court. (See the Bremen case, Section 33.5.1 "Forum-selection clauses"). If that principle is followed by enough national court systems, it could become a principle of customary international lawRules of law derived from the consistent conduct of nation-states acting out of the belief that the law required them to act that way.. As an example, consider that for many years, courts in many nations believed that sovereign immunityA long-standing doctrine under customary international law that recognizes a nation-state’s immunity from legal claims. Although absolute sovereign immunity was widely held through the greater part of the twentieth century, a more restrictive doctrine began to take hold after World War II, one that denied sovereign immunity for a sovereign’s commercial or private acts. was an established principle of international law.

Judicial Decisions in International Tribunals; Scholarly Teachings

The Statute of the International Court of Justice recognizes that international tribunals may also refer to the teachings of preeminent scholars on international law. The ICJ, for example, often referred to the scholarly writings of Sir Hersh Lauterpacht in its early decisions. Generally, international tribunals are not bound by stare decisis (i.e., they may decide each case on its merits). However, courts such as the ICJ do refer to their own past decisions for guidance.

There are many international tribunals, including the European Court of Justice, the ICJ, and the International Criminal Court. Typically, however, disputes between corporations or between individuals that cross national boundaries must be resolved in national court systems or in arbitration. In other words, there is no international civil court, and much complexity in international law derives from the fact that national court systems must often choose from different sources of law, using different legal traditions in order to resolve international disputes. For example, a court in one nation may have some difficulty accepting the judgment of a foreign nation’s court system, as we see in Koster v. Automark (see Section 33.5.2 "Due process in the enforcement of judgments").

Due Process and Recognition of Foreign Judgments

Issues surrounding recognition of foreign judgments arise when one nation’s courts have questions about the fairness of procedures used in foreign courts to acquire the judgment. Perhaps the defendant was not notified or did not have ample time in which to prepare a defense, or perhaps some measure of damages was assessed that seemed distinctly unfair. If a foreign state makes a judgment against a US company, the judgment will not be recognized and enforced in the United States unless the US court believes that the foreign judgment provided the US company with due process. But skepticism about a foreign judgment works the other way, as well. For example, if a US court were to assess punitive damages against a Belgian company, and the successful plaintiff were to ask for enforcement of the US judgment in Belgium, the Belgian court would reject that portion of the award based on punitive damages. Compensatory damages would be allowed, but as Belgian law does not recognize punitive damages, it might not recognize that portion of the US court’s award.

Concerns about notice, service of process, and the ability to present certain defenses are evident in Koster v. Automark. Many such concerns are eliminated with the use of forum-selection clauses. The classic case in US jurisprudence is the Bremen case, which resolves difficult questions of where the case should be tried between a US and German company by approving the use of a forum-selection clause indicating that a court in the United Kingdom would be the only forum that could hear the dispute.

Part of what is going on in Bremen is the Supreme Court’s concern that due process should be provided to the US company. What is fair (procedurally) is the dominant question in this case. One clear lesson is that issues of fairness regarding personal jurisdiction can be resolved with a forum-selection clause—if both parties agree to a forum that would have subject matter jurisdiction, at least minimal fairness is evident, because both parties have “consented” to have the forum decide the case.


The idea that a forum-selection clause could, by agreement of the parties, take a dispute out of one national court system and into another court system is just one step removed from the idea that the parties can select a fair resolution process that does not directly involve national court systems. In international arbitration, parties can select, either before or after a dispute arises, an arbitrator or arbitral panel that will hear the dispute. As in all arbitration, the parties agree that the arbitrator’s decision will be final and binding. Arbitration is generally faster, can be less expensive, and is always private, being a proceeding not open to media scrutiny.

Typically, an arbitration clause in the contract will specify the arbitrator or the means of selecting the arbitrator. For that purpose, there are many organizations that conduct international arbitrations, including the American Arbitration Association, the International Chamber of Commerce, the International Centre for Settlement of Investment Disputes, and the United Nations Commission on International Trade Law. Arbitrators need not be judges or lawyers; they are usually business people, lawyers, or judges who are experienced in global commercial transactions. The arbitration clause is thus in essence a forum-selection clause and usually includes a choice of law for the arbitrator or arbitral panel to follow.

An arbitral award is not a judgment. If the losing party refuses to pay the award, the winning party must petition a court somewhere to enforce it. Fortunately, almost every country that is engaged in international commerce has ratified the United Nations Convention on the Recognition and Enforcement of Arbitral Awards, sometimes known as the New York Convention. The United States adopted this convention in 1970 and has amended the Federal Arbitration Act accordingly. Anyone who has an arbitral award subject to the convention can attach property of the loser located in any country that has signed the convention.

Key Takeaway

Treaties and conventions, along with customary international law, are the primary sources of what we call international law. Disputes involving parties from different nation-states are resolved in national (federal) court systems, and one nation’s recognition and enforcement of another nation’s judicial orders or judgments will require reciprocal treaties or some review that the order or judgment was fairly obtained (that there was due process in the determination of the order or judgment).


  1. At the US Senate website, read about the history of treaties in the United States. What is an “executive agreement,” and why has the use of executive agreements grown so fast since World War II?
  2. Is NAFTA a treaty or an executive agreement? What practical difference does it make if it is one rather than the other?