Article 4 of the Constitution governs the relationships between states and between the states and the federal government. Its four sections require each state to honor the laws, records, and court judgments of the others; protect citizens who travel or move between states; provide for the extradition of fugitives; set the terms for admitting new states and managing federal lands and territories; and guarantee every state a republican government along with federal protection against invasion and domestic violence.
Section 1: Full Faith and Credit
Section 1 requires every state to honor the “public Acts, Records, and judicial Proceedings” of every other state.1Constitution Annotated. U.S. Constitution Article 4 Section 1 A court judgment entered in one state is enforceable in another without relitigating the underlying case. A debtor ordered to pay in Ohio cannot escape that obligation by moving to Florida. Official records such as marriage licenses, birth certificates, and adoption decrees must be treated as valid nationwide.
The Supreme Court set this rule in place early. In Mills v. Duryee (1813), the Court held that an out-of-state judgment must receive the same weight it would carry in the state where it was originally entered. The justices reasoned that treating foreign judgments as merely preliminary evidence would make the Full Faith and Credit Clause “utterly unimportant and illusory,” since common law already gave judgments that much effect.2Constitution Annotated. ArtIV.S1.3.1 Early Precedent on Full Faith and Credit Clause Congress has the power to prescribe how these records are authenticated, and its implementing statute, 28 U.S.C. § 1738, gives properly authenticated records “the same full faith and credit in every court within the United States” as they would carry at home.3Office of the Law Revision Counsel. 28 USC 1738
Child Custody as a Special Case
Custody orders are never truly final because courts can modify them when circumstances change, and that created a loophole: a parent unhappy with a ruling could move and seek a friendlier order elsewhere. Congress closed it with the Parental Kidnapping Prevention Act of 1980, codified at 28 U.S.C. § 1738A, which requires every state to enforce another state’s custody determination and forbids modification except in narrow circumstances.4Office of the Law Revision Counsel. 28 USC 1738A The statute establishes a jurisdictional hierarchy centered on the child’s “home state” and gives the original court continuing jurisdiction as long as the child or a parent still lives there.
Section 2: Rights Across State Lines and Extradition
Section 2’s first clause, the Privileges and Immunities Clause, prevents states from treating out-of-state Americans like second-class citizens. A state must extend to visiting citizens the same fundamental rights its own residents enjoy.5Constitution Annotated. Overview of Privileges and Immunities Clause A state cannot bar nonresidents from working, accessing its courts, owning property, or traveling within its borders.
The foundational case is Corfield v. Coryell (1823), where Justice Bushrod Washington described the protected rights as including “protection by the government; the enjoyment of life and liberty, with the right to acquire and possess property of every kind, and to pursue and obtain happiness and safety,” along with the right to travel between states, bring lawsuits, claim habeas corpus, and be exempt from discriminatory taxes.6University of Chicago Press. Corfield v. Coryell
The clause does not require perfect equality. States can draw distinctions between residents and nonresidents when fundamental rights are not at stake. In Baldwin v. Fish and Game Commission of Montana (1978), the Supreme Court upheld Montana’s practice of charging nonresidents significantly higher elk hunting license fees, reasoning that recreational hunting is not “basic to the maintenance or wellbeing of the Union.”7Justia U.S. Supreme Court. Baldwin v. Fish and Game Commission of Montana, 436 U.S. 371 A state that tried to block nonresidents from earning a living, by contrast, would almost certainly violate the clause, because the right to work is considered fundamental.5Constitution Annotated. Overview of Privileges and Immunities Clause
Interstate Extradition
The second clause of Section 2 addresses fugitives. Upon demand from the governor of the state where the crime occurred, the state where the fugitive is found must deliver that person for return. The rule applies to treason, felonies, and any other criminal charge.8Constitution Annotated. ArtIV.S2.C2.1 Overview of Extradition (Interstate Rendition) Clause
For most of American history, no mechanism existed to force a reluctant governor to comply. An 1861 Supreme Court decision, Kentucky v. Dennison, held that while the duty was mandatory, federal courts had no power to compel a state to perform it. The Court overruled Dennison in 1987 in Puerto Rico v. Branstad, holding that the obligation to surrender fugitives is directly imposed by the Constitution and enforceable in federal court. The asylum state’s governor has no discretion to refuse a proper demand.9Legal Information Institute. Puerto Rico v. Branstad, 483 U.S. 219
Section 2 originally contained a third clause requiring the return of people “held to Service or Labour” who escaped to free states. The Thirteenth Amendment’s abolition of slavery rendered it a dead letter.10Legal Information Institute. U.S. Constitution Annotated – ArtIV.S2.C3.1 Fugitive Slave Clause
Section 3: New States and Federal Property
Section 3 gives Congress the authority to admit new states, with one hard limit: no new state can be carved from an existing state’s territory, and no state can be formed by merging two or more states, without the consent of every state legislature involved and Congress itself.11Constitution Annotated. ArtIV.S3.C1.1 Overview of Admissions (New States) Clause Admission typically begins with Congress passing an enabling act that authorizes a territory to hold a constitutional convention, draft a state constitution, and apply for admission. Congress then votes on a separate resolution to formally admit the state.
The Equal Footing Doctrine
Congress can attach conditions to the admission process, but the Supreme Court has drawn a firm line. In Coyle v. Smith (1911), the Court held that “when a new State is admitted into the Union, it is so admitted with all of the powers of sovereignty and jurisdiction which pertain to the original States, and that such powers may not be constitutionally diminished” by conditions in the enabling act.12Justia U.S. Supreme Court. Coyle v. Smith, 221 U.S. 559 Congress can impose conditions related to matters within federal power, such as management of public lands, but cannot dictate purely internal state decisions like where a state locates its capital.
Equal footing has property consequences too. Under Pollard’s Lessee v. Hagan (1845), each new state automatically gains title to the beds of navigable waterways within its borders upon admission.13Justia U.S. Supreme Court. Pollard’s Lessee v. Hagan, 44 U.S. 212 The federal government retains title only to submerged lands beneath waters that were not navigable at the time of statehood.14Legal Information Institute. Equal Footing Doctrine The distinction still drives disputes over water rights, mineral extraction, and environmental regulation in western states.
Federal Lands and U.S. Territories
Section 3’s second clause, the Property Clause, gives Congress power over federal lands and territories that the Supreme Court has described as “plenary and without limitations.” Congress can sell, lease, preserve, or regulate federal property, and no state law can interfere.15Constitution Annotated. ArtIV.S3.C2.1 Property Clause Generally This is the legal foundation for national parks, military bases, and the hundreds of millions of acres overseen by the Bureau of Land Management.
The Property Clause also governs the five inhabited U.S. territories: Puerto Rico, Guam, the U.S. Virgin Islands, American Samoa, and the Northern Mariana Islands. Because these territories are classified as “unincorporated,” meaning they are under U.S. sovereignty but not considered an integral part of the country, the full Constitution does not automatically apply to their residents. Under the Supreme Court’s Insular Cases from the early twentieth century, only “fundamental” constitutional rights constrain federal power in unincorporated territories. Territorial residents cannot vote in presidential elections and lack voting representation in Congress. Congress has extended many additional rights by statute, including U.S. citizenship for residents of most territories, but those protections exist at Congress’s discretion.
Section 4: Republican Government and Federal Protection
Section 4 makes three promises to the states. The federal government guarantees every state a “Republican Form of Government,” pledges to protect each state against invasion, and commits to defend states against domestic violence when asked.16Congress.gov. Article IV Section 4
The Guarantee Clause ensures that states remain governed through elected representatives rather than by monarchy, military rule, or some other non-republican structure. The Constitution never defines what qualifies, and the Supreme Court has consistently declined to fill in the details. In Luther v. Borden (1849), which involved two rival governments in Rhode Island each claiming legitimacy, the Court held that deciding whether a state government is truly “republican” is a political question for Congress and the President, not the judiciary.17Constitution Annotated. ArtIII.S2.C1.9.3 Luther v. Borden and Guarantee Clause Enforcement has stayed with the political branches ever since.
Protection against invasion is an unconditional federal obligation; the Constitution does not require a state to ask before the federal government responds to a foreign attack. Domestic unrest is handled differently. The text specifies that the federal government intervenes against “domestic Violence” only “on Application of the Legislature, or of the Executive (when the Legislature cannot be convened).”16Congress.gov. Article IV Section 4 For riots or insurrections, the state must request help. Congress has built on this framework through the Insurrection Act, which sets the specific conditions under which the President may deploy federal troops domestically.