What is Common Law?

If you have ever heard someone refer to “common law marriage,” you may have wondered what exactly “common law” means. Black’s Law Dictionary defines it primarily by distinguishing it from the law of legislatures. In other words, it is case law, or law that comes from court decisions.


Legal historians often trace case law all the way back to Roman law, although our modern understanding of this legal system originated most directly in the medieval English courts. These courts developed an early system of case law that relied on legal precedent; in other words, courts were obligated to follow the legal reasoning developed in earlier decisions. The innovation of legal precedent became a cornerstone of modern legal reasoning.

United States Case Law

Case law in the United States is a direct descendant of the English case law that occurred prior to the late eighteenth century, when the United States declared its independence from Great Britain. After independence, American courts developed their own case law concerning legal disputes within the United States.

Comparison to Statutory Law

The most basic way of understanding case law is by distinguishing it from statutory law. State and federal legislatures pass laws that become statutes. The most commonly recognized statutory law is a criminal code. A person who violates that code may then be charged and tried pursuant to the statute. Unlike statutory law, which legislatures create, case law is the product of court decisions. These court decisions may occur in civil or criminal proceedings, and they may be interpretations of statutory law. Most importantly, once a court issues a decision, future courts are obligated to follow that same legal reasoning, or precedent.


One important feature of case law is that it is highly dependent on jurisdiction. For instance, a state court in Maryland is under no obligation to follow state law precedent from a state court in Ohio. Precedent works in a hierarchical structure that mimics the structure of courts in general; once a court issues a ruling, lower courts are bound by that precedent. In some cases, judges may rely on non-binding precedent if there is no direct precedent from within their own jurisdiction.

Underlying Justification and Goals

The theory underlying case law is that courts should strive for fairness in dealings with similarly situated litigants. Ideally, case law provides a record of how courts have ruled on specific legal questions in the past and an indication of how they will continue to rule on similar legal questions in the future. The goal of this system is to produce consistent outcomes for litigants, although critics suggest that the complexity of case law makes such consistency implausible.

Common law, or case law, is the foundation for much modern American law. As law that comes from courts, not legislatures, it is part of a complex legal tradition that touches on both civil and criminal law. By focusing on the logic of past decisions, case law strives to produce a fair and consistent forum for resolving legal disputes.