Law is a set of rules that govern human behavior and keep societal order. It also functions to control power and prevent abuses of that power. Ultimately it promotes social justice and allows for orderly political change, although that latter function is often served by authoritarian regimes rather than democratic ones.

The term law is most commonly used to refer to the system of rules that a particular nation-state recognizes as governing its people and actions. However, it can also refer to the rules and regulations that govern a specific industry or profession. Laws can be established by the government, and they can also be created by private entities such as companies and organizations.

A nation-state’s law system depends on its government, and it can vary greatly from one country to the next. Some nations, such as the United States, employ a common law legal system, which means that judicial decisions are explicitly acknowledged as laws on equal footing with legislative statutes. This principle is known as the doctrine of stare decisis. Other countries, such as Japan, use a civil law system, which rely on written codes that dictate how judges should decide cases.

Law encompasses many fields of study, from constitutional law and international law to family, employment and intellectual property law. Each of these areas has its own sub-fields and specialties, such as tort law, which involves compensation for harmed individuals or their property; criminal law, which concerns offenses against the state; and labor law, which deals with employee rights.