The United States does not have a single body of law. It has fifty state legal systems layered under a federal system, plus local ordinances beneath both. Knowing which level governs a question is often the first practical step in legal research, because the same conduct can be regulated differently depending on where it happens.
The Constitutional Framework
The federal government is one of limited, enumerated powers. Article I, Section 8 of the U.S. Constitution lists Congress's authority, including power over interstate commerce, bankruptcy, patents and copyrights, naturalization, and federal taxation. The Tenth Amendment reserves powers not delegated to the federal government to the states or the people. States, in turn, hold a general police power to protect health, safety, and welfare, which is the source of authority for most criminal, family, and land-use law.
When Federal Law Controls
Federal law governs areas the Constitution assigns to the national government: immigration, bankruptcy, federal crimes, patents and copyrights, securities regulation, federal tax, and matters involving interstate commerce. Federal agencies also issue regulations that carry the force of law, collected in the Code of Federal Regulations (ecfr.gov). Federal courts hear cases arising under the Constitution and federal statutes, and they also hear certain disputes between citizens of different states.
When State Law Controls
States take the lead on family law, marriage and divorce, wills and probate, property, contracts, most crimes, traffic, professional licensing, and education. Each state has its own constitution, statutes, and court rules. That is why a contract clause, a custody rule, or a criminal sentence can differ from one state to the next, and why lawyers often say that the law depends on the jurisdiction.
Where the Two Overlap
Many real-world problems touch both systems. Employment discrimination, for instance, may be covered by federal civil rights statutes and by a broader state anti-discrimination law. Consumer protection, environmental regulation, and wage rules often have both federal and state layers. A person may be able to bring claims under either or both, and the choice of forum can affect procedure, remedies, and timing.
The Supremacy Clause and Preemption
The Supremacy Clause in Article VI makes the Constitution, federal statutes, and treaties the supreme law of the land, and state judges are bound by them even when state law says otherwise. Preemption is the doctrine that describes when federal law displaces state law. It comes in a few forms:
- Express preemption: the federal statute says it overrides state law in so many words.
- Field preemption: federal regulation is so comprehensive that it leaves no room for states to act.
- Conflict preemption: a state law makes it impossible to comply with both, or stands as an obstacle to the federal purpose.
Preemption is not automatic. Courts begin with a presumption that states may exercise their traditional police powers, and they look to the statute's text and structure to decide whether Congress intended to displace state law.
Full Faith and Credit and Choice of Law
Article IV's Full Faith and Credit Clause requires states to respect the public acts, records, and judicial proceedings of other states, which is why a judgment from one state can usually be enforced in another. When a dispute touches several states, courts apply choice-of-law rules to decide whose substantive law governs. These rules vary, so the location of the parties, the events, and the contract can all matter.
Which Court Hears the Case
Subject-matter jurisdiction determines whether a case belongs in federal or state court. Federal courts have federal-question jurisdiction over claims arising under federal law and diversity jurisdiction over disputes between citizens of different states above a statutory amount, currently set at $75,000 by 28 U.S.C. § 1332. State courts are courts of general jurisdiction and hear most disputes. A defendant may sometimes remove a case from state to federal court when federal jurisdiction exists.
| Feature | Federal law | State law |
|---|---|---|
| Source of authority | U.S. Constitution and enumerated powers | State constitution and general police power |
| Typical subjects | Immigration, bankruptcy, patents, federal tax, interstate commerce | Family, property, contracts, most crimes, traffic, licensing |
| Court system | U.S. district courts, courts of appeals, Supreme Court | State trial and appellate courts |
| Where to research | uscode.house.gov and ecfr.gov | The state legislature's official code site |
State Constitutions Can Go Further
A state constitution may protect rights more broadly than the U.S. Constitution, and state courts may interpret their own charters independently. When a federal right sets a floor, a state can sometimes build above it. This is another reason to check state law even when a federal issue is present.
Local Ordinances: The Third Layer
Beneath state law sits local law. Cities, counties, and special districts adopt ordinances on zoning, noise, building permits, business licensing, animal control, and similar day-to-day matters. Local rules cannot contradict a valid state statute or the state constitution, and states may preempt local regulation in specific areas. Even so, an ordinance can impose requirements that a state law does not, so a complete answer often requires checking the municipal code as well as the state code.
When Federal and State Agencies Both Act
Overlap is common at the agency level. Environmental permits, workplace safety, food and drug labeling, and consumer financial products can involve both federal regulators and state counterparts. Sometimes a federal agency delegates primary enforcement to a state program that must meet federal minimum standards. Understanding which agency has authority, and which remedies it can impose, is often as important as knowing which legislature wrote the underlying statute.
How to Research the Right Level
- Identify the subject and ask whether it is traditionally federal, state, or shared.
- For federal law, search the U.S. Code at uscode.house.gov and regulations at ecfr.gov.
- For state law, use the state legislature's official code site.
- For local rules, check the city or county code.
- Where layers overlap, compare the remedies and deadlines each provides.
Sorting out federal, state, and local authority is a common source of confusion, and the answer can change the outcome. If a real dispute or deadline is involved, confirm the governing law with a licensed attorney. This guide is informational only and is not legal advice.