The Five Sources of Federal Law
American law is drawn from five distinct sources: constitutional law, statutory law, treaties, administrative regulations, and the common law. Each sits in a defined hierarchy beneath the Constitution, and each produces a different category of document on this site.
The Constitution is supreme: any statute, regulation, or treaty that conflicts with it can be invalidated by a federal or state court. That power — judicial review — is itself unwritten in the Constitution's text. It was established by the Supreme Court in Marbury v. Madison, 5 U.S. (1 Cranch) 137 (1803), and every exercise of constitutional litigation since traces back to that one ruling.
A statute found unconstitutional does not vanish from the books automatically — it can remain codified for decades after a court invalidates it, removed only by a later act of Congress. Lower courts that continue enforcing it risk reversal; courts that refuse to enforce a statute the Supreme Court has upheld face the same risk in the opposite direction.
Federal Supremacy Has Limits
The Constitution's Supremacy Clause (Art. VI, cl. 2) makes the Constitution, federal statutes, and ratified treaties the supreme law of the land — but only within the scope of the federal government's enumerated powers. The United States operates as a dual sovereign system: each state retains its own constitution, and the federal government holds only the authority the Constitution actually grants it. States may extend their citizens broader rights than the federal Constitution provides, so long as no federal constitutional right is infringed. This is why the bulk of law that governs day-to-day American life — contract, tort, property, family, and most criminal law — is state law, not federal, even though federal law sets the outer boundary.
From Bill to United States Code
A bill may originate from a sitting member of Congress, a campaign proposal, or a citizen petition routed through a representative. Once introduced, it is assigned to a committee, which researches, debates, and may amend it before sending it to the floor for a vote. A bill must pass both the House and the Senate in identical form before reaching the President.
The chambers differ procedurally even though they are constitutionally equal: only the House may originate revenue legislation (Art. I, §7, cl.1); only the Senate acts on treaties and presidential nominations; the House generally proceeds by majority vote while the Senate relies on extended deliberation and debate before a vote is taken.
A signed bill is delivered to the Office of the Federal Register, assigned a Public Law number, and first published as a slip law. At the end of each congressional session, that year's slip laws are compiled chronologically into the Statutes at Large — the session-law record, organized by date of enactment, not subject.
Public laws are then consolidated by subject into the United States Code: 54 titles maintained by the Office of the Law Revision Counsel, reprinted in full every six years with annual cumulative supplements in between. Not every title carries equal legal weight. Titles 1, 3, 4, 5, 9, 10, 11, 13, 14, 17, 18, 23, 28, 31, 32, 35–41, 44, 46, 49, 51, and 54 have been enacted into positive law — for those, the Code's own text is legal evidence of the law. Every other title is merely prima facie evidence; where it conflicts with the underlying Statutes at Large, the Statutes at Large controls. This is the practical difference between the United States Code and the Statutes at Large: one is organized by subject and shows current law as amended, the other is chronological and shows exactly what was enacted, when.
From Rulemaking to Code of Federal Regulations
Congress frequently cannot, or chooses not to, write statutes detailed enough to handle every situation an agency will face — so statutes delegate rulemaking authority to the executive branch instead. That authority is exercised under the Administrative Procedure Act, codified at 5 U.S.C. §§ 551–559. The APA also encompasses the Freedom of Information Act and the Privacy Act of 1974, the statute guaranteeing individuals the right to see, correct, and limit disclosure of federal records held about them.
A proposed rule is published in the Federal Register for public comment; after the comment period, the agency publishes a final rule, also in the Federal Register, which then becomes effective no sooner than 30 days later. Final rules are codified annually into the Code of Federal Regulations — 50 titles, each title divided into chapters (usually one per issuing agency), then parts, then sections, on a staggered quarterly revision schedule: titles 1–16 each January 1, 17–27 each April 1, 28–41 each July 1, and 42–50 each October 1.
The annual GovInfo edition is the official legal text. The continuously-updated eCFR is current as of today but is explicitly not the legally official version — worth knowing if a citation needs to hold up as authoritative rather than merely current.
The Federal Judiciary
Federal courts have no general common-law power. Under Erie Railroad Co. v. Tompkins, 304 U.S. 64 (1938), a federal court hearing a state-law claim under diversity jurisdiction must apply that state's own statutory and decisional law — even where the federal judge disagrees with it — and cannot dictate the content of state law. Federal courts can develop common law only where it's tied to interpreting a constitutional, statutory, or regulatory text actually before them; maritime law is one of the few areas where the Constitution expressly authorizes the older, broader practice.
Binding precedent itself is a relatively modern doctrine — it became practically possible only once a clear federal court hierarchy existed and appellate decisions began being reported consistently and verbatim, developments of the 19th century. Today the rule rests on public policy grounds: predictability and stability are treated as more valuable than the possibility that any one precedent might later look imperfect, a principle the Supreme Court has applied even where individual justices disagree with the underlying rule.
State, Territorial, and Local Law
The fifty states are separate sovereigns, each with its own constitution, legislature, courts, and body of law. State courts handle the overwhelming majority of all litigation filed in the United States each year — traffic, criminal, civil, domestic relations, and juvenile cases combined dwarf the federal courts' docket by a wide margin, per the National Center for State Courts' own published caseload statistics. Residents of American metropolitan areas commonly live under six or more layers of government simultaneously: federal, state, county, city, and one or more special districts, each with its own enacting and regulatory authority subject to the same judicial interpretation as their federal counterparts.