Law is a system of rules, enforced through a set of institutions, used as an instrument to underpin civil obedience, politics, economics and society. Law serves as the foremost social mediator in relations between people. Writing in 350 BC, the Greek philosopher Aristotle declared, "The rule of law is better than the rule of any individual."

Law consists of a wide variety of separate disciplines. Contract law regulates binding agreements which may relate to everything from civil purchase to trading on derivatives markets. Property law defines rights and obligations related to the transfer and title of personal and real property.

Trust law applies to assets held for investment and financial security, while Tort law allows claims for compensation if an individual or their property is injured or harmed. If the harm is criminalised in penal code, criminal law offers means by which the state can prosecute the perpetrator.

Constitutional law provides a framework for the creation of law, the protection of human rights and the election of political representatives. Administrative law regulates the activities the administrative agencies of government, while International law governs affairs between sovereign nation states in activities ranging from trade, environmental regulation or military action.

Legal systems elaborate rights and responsibilities in a variety of ways. A basic distinction is generally made between civil law jurisdictions and systems using common law. In some countries, religion informs the law. Scholars investigate the nature of law through many perspectives, including legal history and philosophy, or social sciences such as economics and sociology.

The study of law raises important and complex issues concerning equality, fairness, liberty and justice. "In its majestic equality", said the author Anatole France in 1894, "the law forbids rich and poor alike to sleep under bridges, beg in the streets and steal loaves of bread." The central institutions for interpreting and creating law are the three main branches of government, namely an impartial judiciary, a democratic legislature, and an accountable executive. To implement and enforce the law and provide services to the public, a government's bureaucracy, the military and police are vital.

While all these organs of the state are creatures created and bound by law, an independent legal profession and a vibrant civil society inform and support their progress.

All legal systems deal with similar issues and behaviors, but each country categorises and identifies its legal standards and principals in different ways.

A common distinction is that between "public law" (a term related closely to the state, and including constitutional, administrative and criminal law), and "private law" (which covers contract, tort and property). In civil law systems, contract and tort fall under a general law of obligations, while 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 may be of greater practical importance.