Law, body of rules governing the relationships between the members of a community and between the individual and the state. In England, the British Commonwealth, and the United States, the law is based upon statute law, or laws enacted by legislative bodies such as Congress, and upon common law, the body of law created by custom and adherence to rules derived from previous judgments. The other main system, civil law, derives from the laws of ancient Rome and relies not on precedent but on a code of rules established and modified only by statute. This is the dominant system in most of Europe and in many other countries of the world.
All major bodies of law break down into 2 divisions, public law and private law. Public law governs matters that concern the state. Private law governs the relationship between individuals (including corporate bodies such as companies).
The first legal system of which we have any detailed knowledge is that of the Babylonian king Hammurabi in 1700 B.C., whose complex code linked crime with punishment and regulated the conduct of everyday affairs. Like the Hebrew Mosaic Law, it treated law as a divine ordinance. The ancient Greeks were probably the first to regard law as made by man for his own benefit. Roman law was based on the Laws of the Twelve Tables, compiled 451–450 B.C.
The Romans developed a complex equity system when these principles became outdated; the Byzantine emperor Justinian I produced the last definitive code in an attempt to clear up resulting difficulties. Much medieval law was based on Church law, although an independent system arose quite early in England. This grew into the common law and spread outwards with the growth of the British Empire. Napoleon revised Roman law as the basis for his Code Napoléon, the model for most subsequent civil law codes. U.S. law grew out of the common law, but has been much modified by the federal system.