Law is a system of rules, usually enforced through a set of institutions. It shapes politics, economics and society in numerous ways. Contract law regulates everything from buying a bus ticket to trading swaptions on a derivatives market. Property law defines rights and obligations related to transfer and title of personal and real property, for instance, in mortgaging or renting a home. Trust law applies to assets held for investment and financial security, such as pension funds. Tort law allows claims for compensation when someone or their property is injured or harmed. If the harm is criminalised in a penal code, criminal law offers means by which the state prosecutes and punishes the perpetrator. Constitutional law provides a framework for creating laws, protecting people's human rights, and electing political representatives. Administrative law relates to the activities of administrative agencies of government. International law regulates affairs between sovereign nation-states in everything from trade to the environment to military action. Law manifests itself throughout the community in many more ways, and serves as the foremost social mediator of relations between people. "The rule of law", wrote the ancient Greek philosopher Aristotle in 350 BC, "is better than the rule of any individual."

Though all legal systems must deal with similar issues, different countries often categorise and name legal subjects in different ways. Quite common is the distinction between "public law" subjects, which relate closely to the state, and "private law" subjects.In civil law systems, contract and tort fall under a general law of obligations and trusts law is dealt with under statutory regimes or international conventions. International, constitutional and administrative law, criminal law, contract, tort, property law and trusts are regarded as the "traditional core subjects", although there are many further disciplines which might be of greater practical importance.

The Rule of Law, in its most basic form, is the principle that no one is above the law. Thomas Paine stated in his pamphlet Common Sense (1776): "For as in absolute governments the king is law, so in free countries the law ought to be king; and there ought to be no other."

In England, the issuing of the Magna Carta was a prime example of the "rule of law." The Great Charter forced King John to submit to the law and succeeded in putting limits on feudal fees and duties.

Perhaps the most important application of the rule of law is the principle that governmental authority is legitimately exercised only in accordance with written, publicly disclosed laws adopted and enforced in accordance with established procedural steps that are referred to as due process. The principle is intended to be a safeguard against arbitrary governance, whether by a totalitarian leader or by mob rule. Thus, the rule of law is hostile both to dictatorship and to anarchy. Samuel Rutherford was one of the first modern authors to give the principle theoretical foundations, in Lex, Rex (1644), and later Montesquieu in The Spirit of the Laws (1748).

In continental Europe and legal thinking, the rule of law has frequently, but not always, been associated with a Rechtsstaat. According to modern Anglo-American thinking, hallmarks of adherence to the rule of law commonly include a clear separation of powers, legal certainty, the principle of legitimate expectation and equality of all before the law.