The four types of law in the United States are criminal law, civil law, administrative law, and constitutional law. They are sorted by the relationship each one governs: criminal law covers the government prosecuting people for offenses against the public, civil law covers disputes between private parties, administrative law covers the rules written and enforced by government agencies, and constitutional law covers the structure of government and the rights people hold against it. Each category has its own purpose, procedures, and standard of proof, and the differences between them affect who can bring a case, what has to be proven, and what the consequences look like.
Criminal Law
Criminal law covers conduct that legislatures have decided is harmful enough to warrant government-imposed punishment. A criminal case is always brought by the government, either a federal or state prosecutor, against the person accused. The victim does not file the case. Crimes are treated as offenses against the public order, not just against the individual harmed.
The consequences range from fines and community service to probation, imprisonment, and in limited circumstances the death penalty. Because so much is at stake, the standard of proof is the highest in the legal system: the prosecution must prove guilt beyond a reasonable doubt. The Supreme Court established this as a constitutional requirement in 1970, grounding it in the due process protections of the Fifth and Fourteenth Amendments. If a juror can point to a reasonable, evidence-based explanation other than guilt, they should vote to acquit.
Felonies and Misdemeanors
Crimes split into felonies and misdemeanors based on the prison time they carry. Under federal law, any offense punishable by more than one year of imprisonment is a felony, and offenses carrying one year or less are misdemeanors.1GovInfo. 18 USC 3559 – Sentencing Classification of Offenses Most states follow a similar structure, though the specific labels and sentencing ranges vary.
Civil Law
Civil law handles disputes between private parties, whether individuals, businesses, or organizations, where one side claims the other caused harm. The person filing the lawsuit is the plaintiff; the person being sued is the defendant. The government is not bringing charges. The goal is not punishment but a remedy, usually money to compensate for the harm.
Common civil disputes include breach of contract, personal injury claims, property disagreements, landlord-tenant conflicts, and divorce. The standard of proof is significantly lower than in a criminal case: the plaintiff only needs to show that their version of events is more likely true than not. This is called preponderance of the evidence. Think of it as tipping the scales just past 50%.
Filing Deadlines
Every civil claim has a deadline. Wait too long after the harm occurred and you lose the right to sue. For federal civil claims created by statutes passed after December 1, 1990, the default deadline is four years from when the claim first arose, unless the specific statute sets a different period.2Office of the Law Revision Counsel. 28 USC 1658 – Time Limitations on the Commencement of Civil Actions Arising Under Acts of Congress State deadlines vary widely by claim type. Personal injury deadlines are often two or three years; written contract disputes may allow much longer. Missing the deadline is one of the easiest ways to lose a valid case before it starts.
When One Event Triggers Both
These categories are not airtight. A single event can produce both a criminal prosecution and a civil lawsuit running on parallel tracks. If a drunk driver causes a serious crash, the state can file criminal charges for driving under the influence, and the injured person can separately sue for medical bills and lost income. The criminal case requires proof beyond a reasonable doubt. The civil case only requires a preponderance of the evidence. That difference explains why someone can be acquitted of a crime and still lose a civil suit over the same incident.
Administrative Law
Administrative law is the body of rules created and enforced by government agencies. Congress often passes broad legislation setting general goals, such as clean air, safe food, or fair workplaces, and then delegates the authority to write detailed, binding regulations to specialized agencies. The Environmental Protection Agency sets pollution standards. The Food and Drug Administration oversees the safety of prescription drugs, medical devices, food products, cosmetics, and tobacco products, among other categories.3U.S. Food and Drug Administration. What Does FDA Regulate? The Occupational Safety and Health Administration writes workplace safety rules. Each agency operates under the same basic legal framework.
How Agency Rules Get Made
The Administrative Procedure Act, originally enacted in 1946, sets the ground rules for how federal agencies create regulations.4Office of the Law Revision Counsel. 5 USC Subchapter II – Administrative Procedure Under its notice-and-comment process, an agency must publish a proposed rule in the Federal Register, give the public an opportunity to submit written feedback, and then consider that feedback before issuing a final rule.5Office of the Law Revision Counsel. 5 USC 553 – Rule Making The process exists to prevent agencies from imposing major new requirements without public input.
Challenging an Agency Decision
If a federal agency oversteps its authority or ignores its own rules, courts can review the action. The standard they apply most often is whether the agency acted in a way that was arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law.6Office of the Law Revision Counsel. 5 USC Chapter 7 – Judicial Review In most situations, you need to exhaust the agency’s own appeals process before a court will hear your challenge. Skipping that step usually gets the case dismissed.
Constitutional Law
Constitutional law flows from the U.S. Constitution and deals with two big questions: how the government is structured, and what rights individuals hold against the government. It is the highest-ranking source of law in the country. Article VI declares the Constitution “the supreme Law of the Land,” meaning any federal statute, state law, or agency regulation that conflicts with it is invalid.7Constitution Annotated. Article VI – Supreme Law – Clause 2
Separation of Powers
The Constitution divides federal power among three branches. Congress makes the laws, the President enforces them, and the courts interpret them. Each branch has specific tools to check the others. The President can veto legislation, Congress controls funding and can impeach officials, and the courts can strike down laws that violate the Constitution. That last power, called judicial review, was established by the Supreme Court in Marbury v. Madison in 1803, where the Court held that Congress cannot pass laws overriding the Constitution and that courts have the final say on what the Constitution means.8Justia. Marbury v. Madison, 5 US 137 (1803)
The Bill of Rights
The first ten amendments, known as the Bill of Rights, protect specific individual liberties against government interference. These include freedom of speech, religion, and the press under the First Amendment; the right to keep and bear arms under the Second; protection against unreasonable searches under the Fourth; the right against self-incrimination and the guarantee of due process under the Fifth; and the right to a speedy trial and legal counsel under the Sixth.9National Archives. The Bill of Rights – What Does It Say The Eighth Amendment bars excessive bail and cruel or unusual punishment. The Ninth and Tenth Amendments make clear that the people and the states retain all rights and powers not specifically handed to the federal government.
Constitutional rights are not absolute. Courts regularly weigh individual liberties against competing government interests, and entire bodies of case law have developed around the boundaries of each amendment. When a court strikes down a law as unconstitutional, it is applying this branch of law.
Two Distinctions That Cut Across All Four
Beyond the four categories, legal professionals use two more distinctions that affect every area of law.
Statutory Law and Common Law
Statutory law is any law passed by a legislature, meaning Congress at the federal level and state legislatures at the state level. These are the written rules found in code books: criminal statutes defining offenses and penalties, tax codes, environmental regulations authorized by statute, and so on.
Common law is judge-made law built through court decisions over time. When a court decides a case, that ruling becomes precedent, a guide future courts are expected to follow when they encounter similar facts. This principle is called stare decisis, Latin for “to stand by things decided.” A lower court is bound by the decisions of the courts above it in the same system, and courts generally follow their own prior rulings as well, though the Supreme Court has noted that precedent is not an “inexorable command” and can be overturned when earlier decisions prove unworkable.
In practice, both systems work together. Legislatures write statutes, and courts interpret what those statutes mean when applied to real disputes. Those interpretations then become part of the common law that guides future cases. Large areas of law, particularly contract and personal injury law, were originally developed entirely through court decisions, with legislatures later stepping in to codify or modify the rules judges had established.
Substantive Law and Procedural Law
Substantive law defines your actual rights and obligations: what counts as a crime, what makes a contract enforceable, what duties a landlord owes a tenant. Procedural law governs the mechanics of enforcing those rights: how a lawsuit gets filed, what evidence is admissible, how a trial proceeds, and what deadlines apply.10Legal Information Institute. Federal Rules of Civil Procedure Rule 1 – Scope and Purpose Criminal cases have their own procedural rules, separate from civil ones. The distinction matters because you can have a perfectly valid substantive claim and still lose if you file in the wrong court, miss a deadline, or fail to follow the right steps. Procedural mistakes are where otherwise strong cases quietly die.