The four main sources of American law are statutes and ordinances, Constitutional law, administrative law and common law. Treaties are also considered a source of law. Most of U.S. law consists primarily of state law, as regulations and bills often differ between states.
Each source of the law is derived from a different authority. Constitutional law derives from the U.S. Constitution. Statutory law is based on written law created by a legislature, as opposed to one person in power. Administrative law refers to the legislative agencies, and common law refers to decisions handed down by judges that establish precedent for future legal decisions.