Law is a system of rules created and enforced through social or governmental institutions to regulate behavior. The rules are designed to ensure that a society adheres to certain values and norms, such as honesty and fairness. The rules are enforced through the state, which may impose sanctions such as fines or imprisonment on those who break the law. Laws can be created by a collective legislature, resulting in statutes, by the executive through decrees and regulations, or by judges, resulting in case law (or precedent, in common law jurisdictions). Private individuals also create legally binding contracts, which are also called laws, for example, contracts regulating the sale of goods and services. Law is a subject of scholarly inquiry in fields such as legal history, philosophy, political science, sociology, and economic analysis. It is a source of many debates and disputes, such as over the nature of justice and the meaning of equality.

It is difficult to define law, since the precise nature of the concept differs according to the different traditions and cultures that constitute the legal systems of the world. However, it is commonly understood to be a set of social restrictions or standards that must be obeyed in order to maintain order and stability and to promote prosperity for the people.

Most societies have a system of law that regulates many aspects of life. The law might be based on a constitution, written or tacit, or the traditions of the region in which it is embedded. The law might govern a wide range of activities, from the granting or denial of a license to conduct business to the regulation of social services and utilities like water, energy, and telecommunications.

From a scientific point of view, the law is complex because it has both a descriptive and a prescriptive dimension: it tells us how people ought to behave or not behave, and what they should require from each other or not require. Unlike other kinds of empirical sciences, such as natural science (as in the law of gravity) or social science (as in the law of supply and demand), it is not possible to verify the content of the law through experimentation.

As a result, the law cannot mandate behaviours that are beyond the limits of human capabilities or force people to do things against their consciences. In addition, the law is dependent on humans and their mental operations, which make it a system of morality, rather than a set of concrete rules. The study of law involves consideration of the underlying assumptions, motivations, and values behind the creation, enforcement, and application of the law. Law is an essential feature of a well-functioning, democratic society. Without it, societies can quickly descend into chaos and violence. The idea that the state should serve the people by enforcing laws that guarantee freedom and prosperity is an objective that unites many nations in the United Nations. The rule of law requires that governments follow principles such as supremacy of the law, accountability to the law, equality before the law, and separation of powers.