Law is a system of rules enforced by social or governmental institutions to regulate behavior and provide justice for members of society. Its precise definition is a longstanding topic of debate, and it has been variously described as a science, an art, or both.

It may be state-enforced, resulting in statutes or decrees, or it can be private, created by a contractual agreement. In some jurisdictions, law is codified in a constitution, while in others it is derived from custom and precedent through judicial decisions. The study of laws is known as jurisprudence.

In the context of the modern state, law can be used to keep the peace and maintain stability, to protect minorities against majorities, to promote social justice, and to manage orderly social change. Some legal systems are more effective at achieving these goals than others. A nation ruled by an authoritarian government, for example, might be able to enforce order and protect a majority population, but it may also oppress minority groups and prevent their participation in political life. The relative success of a particular nation’s laws and governmental institutions in achieving these goals is often determined by the extent to which the laws reflect the beliefs and values of the people it governs.

The idea that there is a scientific way to determine what constitutes law has been criticized by those who assert that such determinations are not necessarily objective and do not take into account the uniqueness of human beings and their environment. Moreover, the emergence of new technologies that allow observers to record their own experiences and make independent assessments of those observations has raised concerns about the validity of traditional scientific methods.

Nevertheless, the notion of law as a scientifically determined process continues to be embraced by some scientists and has become embedded in many academic curricula. The concept of law as a process that is based on an observer’s prediction about the intersection between her own narrative and an external reality has been widely adopted in other fields, including psychology and physics.

Laws are a central aspect of modern societies, but they are not uniformly applied in all countries and regions. Different types of laws exist in the world’s most diverse cultures, and they serve a variety of purposes. The main categories of law are: