Law is a set of rules created by a society or government that form a framework to ensure a peaceful society. These rules are enforced by mechanisms created by the state, and if they are broken sanctions can be imposed. Law is a wide term, and there are many definitions. The most common definition is that law is a set of rules that must be followed or punished by the people of a country, region or civilization.

There are many types of laws, and they are often based on religion, culture or philosophy. These laws deal with issues such as property, crime and finance, among others. Law is a complex concept, and the precise nature of it is subject to longstanding debate.

The idea that law exists to constrain the actions of individuals and institutions has been central to political and legal thought since at least the 4th century bce when Aristotle argued that it is the rule of law that constrains rulers. The concept was elaborated by Montesquieu in the 18th century and has been a key part of Western liberal thinking ever since.

A law can be a statute, or duly enacted legislation by a legislature, such as a national or state parliament; a regulation, or a legally binding directive from a regulator, such as the European Union; or a court decision that has been ruled upon and has gained broader legal weight in future cases, known as “precedent”, or “stare decisis”.

Private law may also exist, which relates to privately owned property, contracts, debts and other areas. Commercial law, for example, deals with transactions such as buying and selling goods and services; intellectual property law protects the ownership of ideas; and criminal law covers crimes such as murder and terrorism. There are also various branches of law that relate to specific activities, such as tort law, which covers claims against individuals for harming them or their property, including automobile accidents and defamation of character; bankruptcy law; and RICO (Racketeer Influenced and Corrupt Organizations) and securities fraud.

Law has an important social role to play, but it is not without its critics. Some philosophers have argued that the very concept of law is flawed, and that it should be replaced by something more democratic and egalitarian. One such theory is that the law should be based on custom, rather than being written down. Other philosophers, such as Hans Kelsen, have pushed for a pure theory of law, in which law is a normative science that describes what must happen, rather than prescribes what should be done.