What Are the Primary Sources of Law in the U.S.?

U.S. law comes from several primary sources: the Constitution, statutes, regulations, court decisions, and treaties. These sources do not all have the same authority, and their effect depends on the level of government, the subject involved, and how courts interpret them. Understanding how they fit together helps explain where legal rules come from and which rules control when they conflict.

Meta description: Learn about the primary sources of law in the U.S., including the Constitution, statutes, regulations, court decisions, treaties, and state and local law.

What Counts as a Primary Source of Law?

A primary source of law is an official legal authority that establishes, states, or applies a legal rule. It may be created by a legislature, government agency, court, or—in the case of the U.S. Constitution—through a formal process of adoption and amendment. Primary sources are different from secondary sources, which explain or analyze the law.

For example, a federal statute published in the United States Code is primary authority. A law review article discussing that statute is secondary authority. A court may find the article useful, but the article does not itself create a binding rule.

The main primary sources in the United States are:

• The U.S. Constitution and state constitutions
• Statutes enacted by Congress, state legislatures, and local legislative bodies
• Regulations issued by government agencies under legal authority
• Judicial decisions interpreting constitutions, statutes, regulations, and common-law principles
• Treaties made by the United States with other nations
• Executive orders and other official directives, within the issuing official’s legal authority

These sources interact. A statute may authorize an agency to issue regulations; a court may interpret both the statute and the regulation; and the Constitution sets limits on what government may do.

The U.S. Constitution

The U.S. Constitution is the nation’s foundational legal document. It establishes the federal government, divides powers among its branches, allocates authority between the federal government and the states, and protects individual rights. Under the Supremacy Clause, the Constitution is the supreme law of the land. Federal statutes and treaties made under the Constitution, along with other valid federal actions, cannot override it.

The Constitution also limits federal authority. Congress generally needs a constitutional basis to legislate, such as its power to regulate interstate commerce or to tax and spend. The Constitution likewise constrains state governments, including through provisions that apply to states directly or through the Fourteenth Amendment.

Amendments are part of the Constitution and have the same constitutional status as its original text. The first ten amendments, known as the Bill of Rights, protect rights such as freedom of speech, religious exercise, and protections for people accused of crimes. Later amendments address issues including citizenship, voting, and the abolition of slavery.

Each state also has its own constitution. State constitutions organize state governments and protect rights under state law. They may offer protections that go beyond the federal Constitution, although they cannot authorize conduct that violates the federal Constitution or other valid federal law.

Statutes: Laws Enacted by Legislatures

A statute is a law enacted by a legislative body. At the federal level, Congress passes bills, which become law after the president signs them or Congress overrides a veto. Congress may also enact a bill without a signature if the constitutional requirements for doing so are met.

Federal statutes are organized by subject in the United States Code (U.S. Code). The Code is a convenient arrangement of general and permanent federal laws, but it is not itself the original act of Congress. The underlying statutes are published in the Statutes at Large. For questions about a law’s original wording, effective date, or amendments, researchers may need to consult the enacted act as well as the Code.

State legislatures enact state statutes, which are compiled in each state’s own code. State laws cover many subjects, including criminal law, family law, property, business regulation, and traffic rules. Local governments may also enact ordinances under authority granted by state law. A city ordinance, for example, may regulate zoning or noise within the city.

Legislatures can amend or repeal statutes, subject to constitutional limits and applicable legal procedures. When a statute conflicts with another law, courts may consider factors such as the authority of the lawmaking body, the laws’ relative scope, and whether a later law was intended to change an earlier one. A lower-level government generally cannot use a statute or ordinance to override a valid higher-level law that controls the same issue.

Regulations: Rules Issued by Government Agencies

Government agencies often have authority to put legislative laws into practice. Congress or a state legislature may establish an agency, set its responsibilities, and delegate authority to issue regulations within defined limits. A regulation is a binding rule adopted through legal procedures; it is not merely informal advice or a general explanation.

Federal regulations are published in the Code of Federal Regulations (CFR), organized by subject. Proposed regulations and final rules are generally published in the Federal Register. The Administrative Procedure Act sets important procedures for federal rulemaking, including public notice and an opportunity to comment for many rules. Particular statutes may create additional requirements or exceptions.

Agencies also publish guidance, manuals, policy statements, and frequently asked questions. These materials may explain how an agency views a law or how it expects to administer a program, but they are not automatically equivalent to a regulation. Their legal effect depends on the document, the agency’s authority, and governing law.

A regulation must stay within the authority granted by the Constitution and the statute that authorizes it. Courts can review agency actions and may set aside actions that violate applicable law or required procedures. The exact standards for review depend on the statute, the type of agency action, and relevant court decisions.

Court Decisions and Common Law

Courts resolve disputes by applying legal rules to facts. Their written opinions may interpret constitutions, statutes, regulations, and earlier decisions. Court opinions are primary sources because they are official rulings that can establish legal principles or determine how existing rules apply.

The United States has both federal and state court systems. Federal courts generally hear cases involving federal law, the U.S. Constitution, disputes between states, and certain other matters defined by law. State courts handle most legal disputes, including many criminal cases, family matters, personal-injury claims, and questions about state law.

Under the doctrine of precedent, a court generally follows relevant decisions from higher courts in the same court system. A U.S. Supreme Court decision on federal law binds lower federal courts and state courts on the federal issue it decides. A state supreme court’s interpretation of that state’s law generally governs courts within that state, unless federal law controls the question.

Not every part of an opinion has equal precedential force. The legal rule necessary to decide a case is often called the holding. Other observations may be persuasive but not binding. Decisions from courts in other jurisdictions can also be persuasive, though they ordinarily do not control a court outside that jurisdiction.

Common law is law developed through judicial decisions rather than enacted as a comprehensive statute. It remains important in areas such as contracts, torts, and property, particularly when statutes do not fully address an issue. However, legislatures can change common-law rules through statutes, within constitutional limits, and statutes may displace common law in specific fields.

Treaties and Other International Agreements

A treaty is a formal agreement between the United States and one or more foreign nations. Under the Constitution, the president makes treaties with the advice and consent of two-thirds of the senators present. Treaties made under the authority of the United States are part of the supreme law of the land, subject to the Constitution.

Not every treaty provision can be applied directly in court without further action. Some provisions are considered self-executing, while others require Congress to pass implementing legislation. A treaty may also be limited by its terms or by reservations made when the United States agreed to it. When a treaty and a federal statute conflict, courts consider the relevant legal rules and the timing and terms of each; neither can override the Constitution.

The federal government also enters international agreements that are not formally ratified as Article II treaties, including congressional-executive agreements and executive agreements. Their authority and domestic effect depend on the legal basis and the agreement’s terms. For a particular dispute, it is important to identify the specific agreement and any implementing legislation rather than assume that all international agreements operate alike.

Executive Orders and Other Official Directives

The president may issue executive orders to manage the executive branch or carry out responsibilities provided by the Constitution or federal statutes. Executive orders can direct federal officials and agencies, but they do not give the president unlimited authority to create law. An order must rest on a valid source of presidential power and cannot override the Constitution or a federal statute.

Governors and other state executives may issue executive orders under authority provided by state constitutions or laws. Their reach varies by state and subject. Agency directives and proclamations can also have legal significance, but their effect depends on who issued them, the authority behind them, and whether required procedures were followed.

Executive orders are generally published in the Federal Register. Their status can change: a later president may revoke or amend an order, Congress may enact a law that affects it, and courts may review its legality.

How the Sources Fit Together

There is no single list that resolves every possible conflict, but several principles help explain the U.S. legal system. The Constitution is supreme. Valid federal law generally takes precedence over conflicting state law when federal law governs the issue. Within a jurisdiction, statutes, regulations, and court decisions must be read together, with each source limited by the authority that created it.

Federalism means that federal and state governments each have areas of authority. Federal law may preempt state law when the Constitution or Congress makes federal rules controlling. Preemption can be express, implied because federal regulation is comprehensive, or based on a direct conflict between federal and state requirements. Whether preemption applies depends on the governing law and the facts.

Courts interpret legal texts using their wording, context, structure, history, and relevant precedents. A regulation may fill in details authorized by a statute, but it cannot lawfully contradict the statute. A court decision may clarify what a statute means, while a later statute can change the rule going forward, subject to constitutional restrictions.

Primary Sources Versus Secondary Sources

Secondary sources help readers understand and locate the law, but they are not themselves the underlying legal authority. Examples include legal encyclopedias, practice guides, textbooks, law review articles, news reports, and explanatory websites. A secondary source may summarize a court decision or describe a statute’s history, but the official text or opinion remains the primary source.

Secondary sources can be valuable starting points, especially for unfamiliar topics. A careful researcher uses them to identify relevant legal authorities, then checks the current primary sources. This matters because laws can be amended, regulations can be revised, and court decisions can be limited or overruled.

Where to Find U.S. Primary Sources of Law

Many official legal materials are available online. Useful starting points include Congress.gov’s Constitution Annotated for constitutional provisions and analysis; the U.S. Code for federal statutes; GovInfo for official federal publications; and the Electronic Code of Federal Regulations for current federal regulations. The Federal Register provides federal rules, proposed rules, and presidential documents.

State legislature and court websites are often the best sources for current state statutes, regulations, and opinions. Local governments commonly publish ordinances on municipal websites. Official sources should be checked for updates, effective dates, and amendments. For a court case, the opinion and its later treatment matter; for a regulation, the enabling statute and current text matter.

These sources explain where U.S. legal rules originate and how they relate. Identifying the right source is the first step; determining whether it applies to a particular situation requires attention to jurisdiction, current text, and the facts involved.