Law is a system of rules enforceable by the state or other authority which regulates behaviour, and it shapes politics, economics, history and society in many ways. It is sometimes viewed as a separate discipline, although it is often treated as part of the broader social science of sociology. Law can be divided into a number of sub-fields. For example, it is possible to divide legal studies into subjects such as criminal law; property law; family law; and labour law. Each of these is a distinct field, but they all interact and overlap.

Law takes on a special role in societies that are organized into nation-states, where the power to make and enforce laws is vested in a particular political class. The main function of law is to serve as a mediator for the relations between those in power and those without it. In many places it also provides a framework for democracy and civil rights for citizens.

The development of law in different cultures has been influenced by both religious traditions and by the need to settle disputes and resolve conflict in society. The most common distinction between law systems is between civil law jurisdictions, where a legislature or other central body codifies their laws and consolidates them into a code, and common law systems, where judge-made precedent is accepted as binding law. Some modern religious communities also have their own legal systems, including Islamic Sharia law.

One important feature of law is that it tends to be of a normative nature, that is, it tells us how people should behave or what they ought to require from others, rather than just telling them what they may do and how they must act. This is in contrast to the descriptive and causal statements found in other disciplines, such as empirical science (as in the law of gravity) or even in the social sciences, where laws describe relationships between variables.

The study of law is a complex business, with the subject involving a great variety of topics and issues. The core subjects are generally considered to be constitutional law; criminal law; and contract law. The latter is an area of particular interest, with its many different facets and the fact that it covers the whole range of transactions between people and businesses. In addition, there are a large number of specialist fields, such as international law; human rights law; and tax law. Each of these requires specific knowledge and skills, which are usually acquired through a law degree and professional training. A distinguished title for a lawyer is Esquire, and a Doctor of Law is an honorific that indicates that the individual has completed a PhD in law. Some lawyers also use a special title, such as barrister or solicitor, to signify their professional identity. Legal practice is overseen by a government or independent regulating body, such as a bar association or law society. In the United States, a lawyer achieves distinct professional identity through specified legal procedures, such as passing a qualifying examination and being admitted to the bar.