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How does common law differ from law created by legislatures?

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President Lyndon B. Johnson signs the Medicare Bill at a table beside former President Harry S. Truman, with Lady Bird Johnson and others standing behind them. — Legislation Former U.S. president Harry S. Truman (right) looking on as U.S. Pres. Lyndon B. Johnson signs the Medicare bill at the Harry S. Truman Library and Museum in Independence, Missouri, July 30, 1965.

The primary distinction between common law and legislation lies in their origin and development.

Common law is a body of law derived from judicial decisions and custom rather than from legislative enactments. It is built upon precedents established in earlier court cases, a system often referred to as stare decisis ("to stand by decided matters"). In this system, judges create law by interpreting existing rules or filling gaps where no statutory guidance exists, effectively making them participants in the lawmaking process.1234

Legislation, by contrast, consists of laws prepared and enacted by legislatures—such as Congress or state assemblies—often with the participation of the executive branch. Legislation is typically used to create a framework for governmental action in new fields, address issues the common law failed to resolve effectively, or codify existing principles into statutes.3567

While legislation can change or override common-law rules, courts remain responsible for interpreting these statutes, which can sometimes extend or restrict their application. Thus, the two systems are deeply intertwined, with common law providing a foundational structure and legislation serving as a primary tool for modern legal reform.346