Act of State Doctrine

The act of state doctrine provides that U.S. courts will not question the validity of an official act of a foreign government fully performed within its own territory. The act of state doctrine is a doctrine of federal common law that is binding on state courts as well as federal courts. There are several exceptions to the doctrine, including one for expropriations in violation of international law created by Congress in the Second Hickenlooper Amendment, 22 U.S.C. 2370(e)(2).

Choice of Law

When a dispute has a connection to more than one jurisdiction, and when the laws of those jurisdictions are materially different, a court must perform a choice-of-law analysis to determine which law to apply. To make this determination, a court will typically apply the choice-of-law rules of the jurisdiction in which it sits. Although choice-of-law rules vary significantly across U.S. states, many courts look to the Restatement (Second) of Conflict of Laws for guidance. The American Law Institute is currently in the process of drafting the Restatement (Third) of Conflict of Laws.

Choice-of-Law Clauses

A choice-of-law clause is a contractual provision that selects a law to govern the contract. These clauses facilitate settlement by identifying the law that will be applied to resolve future disputes, thereby allowing the parties to more accurately assess the strength of potential claims.  They also reduce the costs of litigation by making it unnecessary for a court to conduct a choice-of-law analysis.


The United States is an outlier both in the amount of discovery permitted during litigation in its courts and in its willingness to assist evidence gathering on behalf of foreign and international courts. The readiness of U.S. courts to compel production by foreign parties of evidence located in foreign countries has at times spurred protests by those countries, particularly in the context of antitrust litigation. When that extraterritorial evidence is in the hands of a nonparty, U.S. courts must seek assistance from the country where the evidence is located because a court can only compel persons subject to its authority to testify or produce documents. To request such assistance, U.S. courts may invoke the Hague Evidence Convention or rely on letters rogatory, both of which are imperfect mechanisms. Meanwhile, Congress has broadly authorized the federal courts to assist with discovery on behalf of foreign or international tribunals through 28 U.S.C. § 1782.


Extraterritoriality refers to the application of a nation’s law to persons, conduct, or property outside its own territory. Customary international law allows nations to regulate extraterritorially on a number of different bases, including effects, nationality, and universal jurisdiction. Nations generally limit the extraterritorial application of their laws to a greater extent than customary international law requires. For example, the United States applies a presumption against extraterritoriality to federal law and sometimes imposes additional limitations as a matter of prescriptive comity. Some U.S. states have their own presumptions against extraterritoriality, which may differ from the federal presumption.

Family Law

International family law focuses on two discrete areas of international practice: (1) private international law, and (2) comparative family law. Key topics include marriage, divorce, custody and movement of children, child support, spousal support, and financial rights and remedies. In addition, there are some areas of developing law, such as parentage and family formation (for example, through adoption or surrogacy) and unmarried partnership rights.

Foreign Judgments

In the United States, the recognition and enforcement of foreign-country judgments is generally governed by state law. Most states have adopted one of two Uniform Acts that provide for the recognition and enforcement of foreign money judgments subject to certain exceptions, including lack of jurisdiction, fraud, and public policy. There is also a federal statute, the SPEECH Act, that governs the recognition and enforcement of foreign defamation judgments. The United States has signed two judgments treaties, the 2005 Hague Convention on Choice of Court Agreements and the 2019 Hague Judgments Convention, but neither has yet been sent to the Senate for ratification.

Foreign Official Immunity

Foreign official immunity refers to international and domestic rules that shield foreign officials from suit. Diplomatic and consular immunity are governed by the Vienna Convention on Diplomatic Relations and the Vienna Convention on Consular Relations, respectively. Under customary international law, “head-of-state” immunity provides absolute immunity to sitting heads of state, heads of government, and foreign ministers, whereas “conduct-based” immunity shields lower-level officials and former officials from suits based on acts taken in their official capacities. In the United States, head-of-state and conduct-based immunity are rules of federal common law.

Foreign Sovereign Immunity

Customary international law provides immunity to states from the jurisdiction of foreign national courts. The immunity extends to state agencies and to state-owned property, protecting them from adjudicatory jurisdiction and from enforcement measures. Foreign sovereign immunity has important exceptions, including for waiver, for some conduct or property related to commercial activity, and for some torts committed on the territory of the forum state. In the United States, all aspects of foreign sovereign immunity for cases in state or federal court are governed by a federal statute, the Foreign Sovereign Immunities Act.

Foreign State Compulsion

Foreign state compulsion (also called foreign sovereign compulsion) is a doctrine allowing a U.S. court to excuse violations of U.S. law on the ground that they are compelled by foreign law. The doctrine arises most often when foreign law blocks compliance with U.S. discovery requests and in certain substantive areas like antitrust law. It generally requires the risk of severe sanctions under foreign law and a good faith effort by the person in question to avoid the conflict.

Forum Non Conveniens

Forum non conveniens is a judge-made doctrine that permits a court to decline to hear a case on the understanding that it would be more appropriately resolved by a different sovereign’s courts. The doctrine is used by both state and federal courts in the United States to dismiss cases with transnational elements, particularly those brought by non-U.S. plaintiffs.

Forum Selection Clauses

A forum selection clause is a contractual provision that selects a specific court to resolve disputes. When suit is filed in a jurisdiction that is not the chosen forum, the clause may provide a basis for dismissal or transfer. When suit is filed in the chosen forum, the clause may provide a basis for asserting personal jurisdiction over the defendant.

Human Rights Litigation

Victims of human rights violations sometimes bring claims in U.S. courts, including claims based on violations outside the United States. The U.S. Supreme Court has recognized a limited cause of action for human rights claims under the Alien Tort Statute. Congress has also enacted statutory causes of action such as the Torture Victim Protection Act (TVPA) and the Trafficking Victim Protection Reauthorization Act (TVPRA). Human rights claims against individuals often raise questions of foreign official immunity.

International Comity

International comity refers to deference to other countries that is not required by international law. The principle of international comity animates many different doctrines, which can be grouped into three categories: those that defer to foreign governments as litigants (“sovereign party comity”), those that defer to foreign lawmakers (“prescriptive comity”), and those that defer to foreign courts (“adjudicative comity”). Within each of these categories, “positive” comity doctrines use comity as a principle of recognition (such as the recognition of foreign judgments or the application of foreign law), while negative comity doctrines use comity as a principle of restraint (such as foreign sovereign immunity or the act of state doctrine).

Judicial Assistance Treaties

Since the late 1800s, states have used treaties to simplify the process of cross-border litigation. The Hague Conference on Private International Law has promulgated dozens of such conventions. Major Hague treaties to which the United States is a party address such issues as service of process [link to resource page], discovery and evidence gathering [link to resource page], the certification of public records, and family law issues like divorce, custody, and child support. The United States has also signed but not yet ratified two recent Hague treaties: the 2005 Choice of Court Convention and the 2019 Judgments Convention. The United States is also party to many Mutual Legal Assistance Treaties, which generally apply only to criminal cases.

Parallel Proceedings

A proceeding is parallel if it involves similar parties and similar issues. The U.S. Supreme Court has not yet addressed how federal courts should assess parallel proceedings in foreign courts (sometimes referred to as lis alibi pendens). The default approach has been to allow both cases to proceed until a judgment has been rendered in one case that may be given preclusive effect in the other. Most federal courts treat this question as one of abstention, though occasionally courts address it through forum non conveniens.

Personal Jurisdiction

Personal jurisdiction over foreign defendants in state courts is limited by state statutes and by the Due Process Clause of the Fourteenth Amendment of the U.S. Constitution, which the Supreme Court has interpreted to require that defendants have “minimum contacts” with the forum state. Personal jurisdiction in federal courts extends in most cases only as far as the jurisdiction of the state courts of the state in which they sit.  However, in limited situations governed by Federal Rule of Civil Procedure 4(k)(2) and some federal statutes, personal jurisdiction in federal courts may extend beyond the limits of state court jurisdiction. Personal jurisdiction in federal courts is limited by the Fifth Amendment’s Due Process Clause, the scope of which remains unclear. Whether customary international imposes general limits jurisdiction on jurisdiction to adjudicate is also unclear.

Service of Process

Service of process both provides a defendant with notice of a lawsuit and asserts the court’s authority over the defendant. Proper service is necessary to obtain a judgment that will be recognized in other jurisdictions. In the United States, service can be accomplished through private parties. Many foreign states, however, regard service as a public act that can only be effectuated by government officials. That difficulty is addressed by the Hague Service Convention, to which the United States is a party and with which compliance is mandatory when a case falls within its scope.

State Law

Despite suggestions that federal law should govern all relations with other countries, state law and state courts play a prominent role in transnational litigation. State law governs the enforcement of foreign judgments and the choice of law for state-created causes of action. State courts apply their own doctrines of forum non conveniens. And the Federal Rules of Civil Procedure incorporate state law on questions from personal jurisdiction to service of process.

Transnational Litigation

Transnational litigation is litigation involving persons, events, or transactions with a connection to more than one country. In the United States, transnational litigation may occur in state or federal court.  The term encompasses ordinary commercial disputes between parties in different nations, multi-jurisdictional patent wars, and claims based on international human rights law. Transnational litigation cases raise a host of unique issues relating to procedural rules, private contracts, federal statutes, state law, and international treaties.