What are the three main sources of law in the U.S.?

• A. Federal law, state law, and common law.
• B. Federal law, international law, and tribal law.
• C. State law, municipal ordinances, and case law.
• D. Constitution, statutes, and regulations.

Answer: (A)

Understanding how law is created across different levels helps explain why this trio is considered the main source. Federal law includes the Constitution, statutes passed by Congress, and binding federal regulations. State law covers similar material at the state level—state constitutions, statutes, and regulations. The third element comes from the decisions of courts, i.e., case or common law, which develops rules through judicial interpretation and fills gaps where statutes or regulations don’t address a specific issue. Together, these streams—federal authority, state authority, and the judicially developed rules—form the foundation of how law operates in the United States.

Other options mix in areas that don’t function as the primary, overarching sources domestically: international law doesn’t automatically govern U.S. private rights without enabling legislation, tribal law applies within tribal jurisdictions, and municipal ordinances are local rules rather than broad, nationwide sources. While constitutional provisions, statutes, and regulations are essential components of the legal system, the combination of federal law, state law, and common law best captures the broad, layered sources that guide most legal outcomes in the U.S.