An essential purpose of the Full Faith and Credit Clause is to assure that the courts of one state will honor the judgments of the courts of another state without the need to retry the whole cause of action. It was an essential mechanism for creating a “union” out of multiple sovereigns. The first sentence of the Full Faith and Credit Clause appeared almost verbatim in Article IV of the Articles of Confederation, which read: “Full faith and credit shall be given in each of these States to the records, acts and judicial proceedings of the courts and magistrates of every other State.” But while “faith and credit” was a familiar evidentiary term, early courts disagreed on whether the Articles obliged states merely to receive each other’s documents in evidence, or also to treat such documents, once admitted, as conclusive on the merits. In 1781, a committee of the Confederation Congress tried to obtain clarification from the states on how they treated other states’ official documents and judgments.

At the Constitutional Convention, the Framers rejected a proposal that would have required each state to enforce the other states’ judgments regarding debts. Instead, it adopted the Confederation clause almost verbatim but added a second sentence giving Congress power over the “manner of authentication” and the documents’ “effect.” Moreover, the “public Acts” requirement was apparently added to force state courts to enforce each other’s insolvency laws.

Because the clause was drawn from the Articles of Confederation, there is very little discussion of it in the The Federalist Papers, although James Madison asserted in No. 42 that its clarity was a great improvement over the version in the Articles. He listed the clause as one of several that “provide for the harmony and proper intercourse among the States.”

It seems clear that a major purpose of the clause was to prevent a judgment debtor (i.e., someone who had been found financially liable by a court) from evading his creditors by crossing into other states. In the colonial courts, a judgment creditor from another colony would have to prove the other colony’s court’s judgment as an issue of fact—and might even have to relitigate the merits, with the old judgment given only prima facie effect.

While it is possible to read the clause’s first sentence (and the word “full”) to require conclusive effect for all state records, the dominant view at the Founding was that any additional substantive effect was for Congress to determine. In The Federalist No. 42, James Madison emphasized Congress’s power, describing the Article’s language (and thus the new clause’s first sentence) as “extremely indeterminate” and “of little importance under any interpretation which it will bear.” This echoed James Wilson’s argument at the Constitutional Convention, that the clause would be largely useless “if the Legislature were not allowed to declare the effect,” as it “would amount to nothing more than what now takes place among all Independent Nations.”

Congress first exercised its power in 1790, specifying the mode of authentication in the Full Faith and Credit Statute (1 Stat. 122). That statute gave properly authenticated court records, in particular, “such faith and credit” in other states as they had at home. But this only produced disputes over whether “such faith and credit” referred to evidentiary admissibility, or whether it made each state’s court records equally conclusive in other states. The Supreme Court adopted the equally-conclusive view in Mills v. Duryee (1813), but as a construction of the act of Congress, not of the Constitution.

Over time, the Court began to merge the statutory and constitutional inquiries—treating the substantive effect of judgments as determined by the Constitution itself, following a suggestion made by Justice Joseph Story in his Commentaries on the Constitution of the United States (1833). The Court eventually read the Constitution to extend conclusive effect to state laws, which the 1790 statute had pointedly not required. Chicago & Alton Railroad v. Wiggins Ferry Co. (1887). When Congress recodified the statute in 1948, it amended its language to accord with the Supreme Court’s view.

The Supreme Court has continued to use the broad view of the clause’s effect to develop a detailed jurisprudence, policing state court proceedings in three contexts: (1) determining when a state must take jurisdiction over claims that arise in other states, (2) limiting the application of local state law over another state’s law in multi-state disputes, and (3) recognizing and enforcing judgments rendered in sister-state courts.

First, the Court has obliged state courts to hear claims that arise under sister-state laws, at least where the courts recognize the equivalent claim is based on local law. Hughes v. Fetter (1951). A state may also not attempt to monopolize litigation by requiring that enforcement actions be heard solely in its own local courts. Tennessee Coal, Iron & Railroad Co. v. George (1914); Crider v. Zurich Insurance Co. (1965).

Second, the Supreme Court has also restricted state courts’ ability to apply their own laws to multistate disputes. State courts may almost always apply their own procedural rules, including their own statutes of limitations, but there are times when a state’s substantive law should give way to the substantive law of another state, under what is called “choice of law.” It was Justice Story who first seriously explored this issue in his Commentaries on the Conflict of Laws, Foreign and Domestic (1834). In the early twentieth century, the Court began to treat these doctrines as mandated by the Constitution. Initially, the Court required the states to adhere to the traditional territorial principles (lex loci) in the choice of law. Thus, if particular legally designated events of a dispute happened in a particular state, say Massachusetts, but the dispute came to trial in Pennsylvania, the Pennsylvania court had to apply Massachusetts law. Western Union Telegraph Co. v. Brown (1914); New York Life Insurance Co. v. Dodge (1918). Later, the Court allowed a state to apply its own substantive law whenever it had a legitimate interest in the outcome of the case. Pacific Employers Insurance Co. v. Industrial Accident Commission (1939). The most recent Supreme Court cases have collapsed Due Process Clause and Full Faith and Credit Clause inquiries into a single requirement for the application of “forum law” (the law of the state where the case is being heard): “that state must have a significant contact or significant aggregation of contacts, creating state interests, such that choice of its law is neither arbitrary nor fundamentally unfair.” Allstate Insurance Co. v. Hague (1981).

With this shift in tests, the Court has backed away from constitutional scrutiny of state court choice-of-law decisions. In fact, the Court has even allowed one state to sue another state in the first state’s courts despite the defendant state’s sovereign immunity laws. State of Nevada v. Hall (1979); Franchise Tax Board of California v. Hyatt (2003). Moreover, the Court has only once in the last fifty years limited a state’s ability to apply its own law. Phillips Petroleum Co. v. Shutts (1985).

Third, although the Court has largely backed away from policing state choice-of-law decisions, it has imposed stringent requirements regarding recognition and enforcement of sister-state judgments. Practical interests usually require each state to recognize and enforce almost all final court judgments rendered by sister states, even those that offend the public policy of the enforcing state. Pursuant to Congress’s implementing statute of the Full Faith and Credit Clause, the enforcing state’s courts must give judgments at least as much effect as the rendering state would. Nonetheless, states can still apply their own statutes of limitations when enforcing judgments by other states’ courts, and state administrative decisions that are not reviewed by a court are not entitled to respect in other states.

The Court has recognized a few relatively narrow policy-based exceptions to the states’ obligations to enforce the judgments of other states’ courts. First, a defendant who did not appear in the first proceeding can collaterally attack a judgment against him on the grounds that the first state’s courts lacked personal jurisdiction over the defendant. Second, states are not permitted directly to affect land titles in other states by, for example, issuing a deed to land located in another state. Third, judgments based on purely penal claims (i.e., criminal or administrative fines) need not be enforced by other states. To fall into this penal exception, the judgment must be for the purpose of punishment rather than compensation, and the recovery must be in favor of the state, not a private individual. But tax judgments, judgments for punitive damages in favor of private plaintiffs, and compensatory tort judgments in favor of the state all fail to qualify for this penal exception. Fourth, state courts enforcing an out-of-state court judgment can apply their own evidentiary rules. For example, the enforcing state may accept testimony that would have been illegal under the other state’s law. Finally, if a state court issues a divorce decree in an ex parte proceeding (where only one spouse appears), the absent spouse can collaterally attack the validity of the present spouse’s domicile within the rendering state.

Congress has invoked its full faith and credit authority in certain specific contexts related to marriage, divorce, and children. When it acts, Congress presumably displaces Supreme Court Full Faith and Credit precedents in these areas. Under the congressional acts, a state court may modify a sister-state court’s child-custody and support orders to suit “the best interests of the child.” The Parental Kidnapping Prevention Act of 1980 (28 U.S.C. § 1738A) attempts to fix jurisdiction over child-custody determinations and requires states that lack jurisdiction under the act to enforce valid custody orders. The Full Faith and Credit for Child Support Orders Act of 1995 (28 U.S.C. § 1738B) allocates jurisdiction over the rendering of child-support orders and specifies states’ enforcement obligations.

Finally, when it appeared that Hawaii might recognize the validity of same-sex marriages, Congress responded in 1996 with the Defense of Marriage Act (DOMA) (28 U.S.C. § 1738C). Section 2 of DOMA permits each state to refuse to give effect to other states’ acts, records, and judicial proceedings respecting same-sex marriages. Moreover, the act specifically enables each state to deny rights and claims arising from same-sex marriages created in other states. Section 3 of DOMA, which defines marriage as consisting only of unions between a man and a woman for purposes of federal law and federal benefits, does not implicate the Full Faith and Credit Clause. Nonetheless, in United States v. Windsor (2013), the Court struck down section 3 as violative of the Due Process Clause of the Fifth Amendment on the grounds that it was based on an animus against those persons whose same-sex marriages had been validated by state law. However, section 2 (pertaining to full faith and credit) has not been the subject of constitutional attack by any branch of the federal government.