What Are the Sources of Law?

Efficient legal research starts first with an understanding of the sources of law in the United States.

• Constitutional law: The federal government and all the states have constitutions whose primary purpose is to establish the government and define its functions and obligations in relation to the people.
• Statutory law: Laws established by legislative action.
• Administrative regulations: Administrative agencies (IRS, FDA, FAA, etc.) have the power to make necessary rules and regulations.
• Ordinances: Laws established by a local government such as a county board of supervisors or city council.

Case law: Laws are created in the form of decisions, also called opinions, that are published in case reporters. Case law is also known as common law and is based on the legal principle known as stare decisis (let the decision stand). Simply put, courts are required to follow earlier decisions made by higher courts, such as the Supreme Court. This helps make the law predictable.