Sources of U.S. Law: Constitutional, Statutory, Regulatory, and Common Law

The United States legal system draws authority from four distinct and interacting sources: constitutional text, legislative statutes, administrative regulations, and judge-made common law. Understanding how these sources operate, how they rank against one another, and where they conflict is foundational to navigating any legal question in a U.S. context. This page provides a structured reference covering definitions, structural mechanics, classification boundaries, and common points of confusion across all four source categories.

• Definition and scope
• Core mechanics or structure
• Causal relationships or drivers
• Classification boundaries
• Tradeoffs and tensions
• Common misconceptions
• Checklist or steps (non-advisory)
• Reference table or matrix

Definition and scope

The phrase "sources of law" refers to the formal origins from which legally binding rules derive their authority and enforceability within a jurisdiction. In the United States, four primary sources collectively constitute the full body of enforceable law:

Constitutional law consists of rules derived from the U.S. Constitution, ratified in 1788, and its 27 amendments, as well as the constitutions of each of the 50 states. The Constitution establishes the framework of government and sets outer limits on what other legal actors — Congress, state legislatures, administrative agencies — may do. Article VI, Clause 2 of the Constitution (the Supremacy Clause) establishes that federal constitutional provisions override conflicting state law.

Statutory law consists of written enactments passed by a legislative body — Congress at the federal level or state legislatures at the state level. Federal statutes are codified in the United States Code (U.S.C.), maintained by the Office of the Law Revision Counsel. Title 18 of the U.S.C. covers federal criminal offenses; Title 42 covers civil rights and public health provisions.

Regulatory law (also called administrative law) consists of rules promulgated by executive branch agencies under authority delegated by statute. The Administrative Procedure Act of 1946 (5 U.S.C. §§ 551–559) governs how federal agencies create binding rules and adjudicate disputes. Final rules are published in the Federal Register and codified in the Code of Federal Regulations (C.F.R.), which comprises 50 titles organized by subject matter.

Common law consists of judicially created legal principles derived from court decisions rather than legislative enactments. Under the doctrine of stare decisis, courts are bound to follow prior decisions of higher courts within the same jurisdiction. English common law forms the historical foundation, adopted by most states at the time of independence, though Louisiana follows a civil law tradition derived from French and Spanish codes.

For broader context on how these sources interact within the court hierarchy, see Structure of the U.S. Court System.

Core mechanics or structure

The hierarchy of authority

When sources conflict, a defined hierarchy of supremacy resolves the conflict:

1. U.S. Constitution (supreme law)
2. Federal statutes (must comply with the Constitution)
3. Federal regulations (must comply with their authorizing statute and the Constitution)
4. State constitutions (supreme within the state, subordinate to federal law)
5. State statutes
6. State regulations
7. Common law (fills gaps where no enacted law governs)

This hierarchy means a federal agency regulation that exceeds its statutory authorization is void, as confirmed by the Supreme Court's framework established in Chevron U.S.A., Inc. v. Natural Resources Defense Council, 467 U.S. 837 (1984), and subsequently modified by Loper Bright Enterprises v. Raimondo, 603 U.S. ___ (2024), which eliminated mandatory judicial deference to agency statutory interpretations.

How statutes become law

Under Article I of the Constitution, federal legislation requires passage by both chambers of Congress and presentment to the President. The President may sign the bill, allow it to lapse into law after 10 days, or veto it — a veto that Congress can override with a two-thirds majority in both chambers (Article I, Section 7).

How regulations are created

Federal agencies follow the notice-and-comment rulemaking process prescribed by the Administrative Procedure Act. A Notice of Proposed Rulemaking (NPRM) is published in the Federal Register, a public comment period of at least 30 days is required (though 60 days is common for significant rules), and agencies must respond to substantive comments before issuing final rules. Executive Order 12866 (1993) requires the Office of Information and Regulatory Affairs (OIRA) to review economically significant rules — defined as those with an annual economic effect of $100 million or more.

How common law evolves

Judicial decisions create precedent through the principle of stare decisis. Only decisions from a court's own jurisdiction and from higher courts within that jurisdiction carry binding authority; decisions from courts in other jurisdictions carry persuasive authority only. The distinction between binding and persuasive precedent is fundamental to legal research. For more on how courts apply these principles, see Common Law and Case Precedent.

Causal relationships or drivers

The four-source structure of U.S. law did not arise arbitrarily. Three structural forces explain its shape:

Federalism divides lawmaking authority between federal and state governments, producing parallel bodies of constitutional, statutory, regulatory, and common law at each level. This dual structure means a single set of facts can implicate federal and state law simultaneously. The scope of federalism and U.S. law directly determines which source governs a given dispute.

Separation of powers allocates lawmaking, execution, and adjudication to distinct branches. Congress enacts statutes; the executive branch implements them through agencies and regulations; courts interpret and apply both. When one branch exceeds its allocated role, legal challenges arise under constitutional law — most often the Nondelegation Doctrine or the Appointments Clause (Article II, Section 2).

Common law gap-filling exists because legislatures cannot anticipate every factual scenario. Where no statute or regulation speaks to a matter, courts apply common law principles developed through prior decisions. This is why contract disputes, tort claims, and property disputes remain heavily governed by common law even in jurisdictions with detailed statutory codes.

Classification boundaries

Determining which source of law applies to a given question requires attention to three boundary problems:

Federal vs. state law: The Supremacy Clause preempts state law in three configurations — express preemption (Congress explicitly displaces state law), field preemption (federal regulation is so pervasive that state law has no room to operate), and conflict preemption (compliance with both laws is physically impossible or state law obstructs federal objectives). The Supreme Court addressed all three forms in Altria Group, Inc. v. Good, 555 U.S. 70 (2008).

Statute vs. regulation: Statutes set policy; regulations supply operational detail. A regulation cannot exceed its authorizing statute. If Congress grants an agency authority to regulate "air pollutants," the agency cannot extend that authority to regulate greenhouse gases without a clear statutory basis — as litigated in West Virginia v. EPA, 597 U.S. 697 (2022), which applied the Major Questions Doctrine to invalidate EPA's Clean Power Plan rule.

Common law vs. statutory override: Legislatures can abrogate common law rules by statute. Many state tort reform acts, for example, modify or cap common law damages. Once a legislature speaks, statutory text controls — common law fills gaps that statute leaves open, not gaps the statute explicitly addresses.

Tradeoffs and tensions

Democratic legitimacy vs. technical expertise

Statutes are passed by elected legislators, giving them strong democratic legitimacy. Regulations are drafted by agency staff — many of them career civil servants — with deep technical knowledge but without direct electoral accountability. The tension between these values underlies the long-running debate over administrative deference, resolved most recently by the Supreme Court in Loper Bright (2024), which shifted interpretive authority over ambiguous statutory language from agencies back to courts.

Stability vs. adaptability

Stare decisis promotes predictability but can entrench outdated rules. Constitutional amendments require ratification by three-fourths of the 50 states (38 states) under Article V — a deliberate supermajority threshold that creates inertia. Common law, by contrast, can evolve through judicial decisions without legislative action, providing adaptability at the cost of uniformity.

Uniformity vs. state autonomy

Federal statutory uniformity benefits interstate commerce and civil rights enforcement. State autonomy enables legal experimentation — different states may adopt different approaches to contract default rules, negligence standards, or privacy protections. This tension is structurally unresolved; it is managed case-by-case through preemption doctrine.

Common misconceptions

Misconception: Executive orders are laws passed by Congress.
Correction: Executive orders carry the force of law within the executive branch and over federal agencies, but they derive authority from the President's constitutional powers or from statutory delegation — not from congressional enactment. Congress can negate the effect of an executive order through legislation.

Misconception: Regulations and statutes are the same thing.
Correction: A statute is an act of Congress. A regulation is a rule issued by an executive agency under authority delegated by statute. They occupy different levels of the legal hierarchy, and regulations are invalid if they contradict their authorizing statute.

Misconception: Common law is unwritten and therefore informal.
Correction: Common law is written — it appears in judicial opinions published in official and commercial reporters. "Unwritten" historically referred to law not enacted by a legislature, not to law that is undocumented. The Federal Reporter, the regional reporters, and state court reporters preserve the written record of common law development.

Misconception: The U.S. Constitution is the only constitution that matters.
Correction: Each state has its own constitution. State constitutions can provide broader individual rights than the federal Constitution — they cannot provide narrower ones. The California Constitution, for example, contains an explicit right of privacy (Article I, Section 1) with no direct federal constitutional equivalent.

Misconception: Federal law always supersedes state law.
Correction: Federal law supersedes state law only in areas of federal constitutional authority. The Tenth Amendment reserves powers not delegated to the federal government to the states or to the people. Outside enumerated federal powers, state law governs.

Checklist or steps (non-advisory)

The following sequence describes the analytical steps typically followed when identifying which source of law governs a legal question. This is a descriptive reference framework, not legal advice.

Step 1 — Identify the subject matter.
Determine whether the matter involves a constitutional right, a statutory entitlement, a regulatory requirement, or a common law claim (tort, contract, property).

Step 2 — Identify the applicable jurisdiction.
Determine whether the governing law is federal, state, or both. Consult the federal vs. state court jurisdiction page for Federal vs. State Court Jurisdiction.

Step 3 — Apply the hierarchy.
Check for constitutional provisions that bear on the question. Then check for applicable federal statutes (U.S.C.). Then check for applicable federal regulations (C.F.R.). Then check state equivalents.

Step 4 — Check for preemption.
If both federal and state law apply, analyze whether federal law expressly or implicitly preempts state law in the relevant field.

Step 5 — Identify controlling case law.
Search for binding precedent from the applicable jurisdiction's highest court and intermediate appellate courts. Note the distinction between holding (binding) and dicta (non-binding) within prior opinions.

Step 6 — Identify persuasive authority.
Where controlling precedent is absent or unclear, identify persuasive authority — decisions from other circuits, secondary Restatements (published by the American Law Institute), or treatises.

Step 7 — Synthesize the rule.
Combine constitutional limits, statutory text, regulatory requirements, and applicable common law into a unified statement of the governing legal standard.

Reference table or matrix

References

• U.S. Constitution — National Archives
• United States Code — Office of the Law Revision Counsel
• Code of Federal Regulations — Electronic Code of Federal Regulations (eCFR)
• Federal Register — National Archives
• Administrative Procedure Act, 5 U.S.C. §§ 551–559 — eCFR
• Office of Information and Regulatory Affairs (OIRA) — Executive Order 12866
• American Law Institute — Restatements of the Law
• Supreme Court of the United States — Opinion Archive
• West Virginia v. EPA, 597 U.S. 697 (2022) — Supreme Court
• Loper Bright Enterprises v. Raimondo, 603 U.S. ___ (2024) — Supreme Court