Law is the set of rules enacted or enforced through societal or government institutions to govern behaviour. It may be a collection of statutes, regulations and judicial decisions. It may also be the code of a profession such as medicine or a branch of knowledge such as philosophy. It can also refer to the practice of law, that is the profession of advising people on legal matters and representing them in court.

There are three main categories of law: criminal, civil and corporate. Criminal law covers offences against a person or property, such as burglary and murder. Civil law covers disputes between individuals, such as car accidents and defamation of character. Corporate law, in turn, deals with the regulation of corporations and their financial activities. These include stock market listings and mergers, the setting of minimum capital standards and rules about best practice for investment.

In terms of its social impact, law encompasses all aspects of human rights and the distribution of power between different parts of a society. It is important for a society to have an even playing field, so that wealth and social class do not determine whether someone is more likely to be able to get away with breaking the law. It is also necessary for a society to have checks on the power of a government, such as regular elections and procedures like no confidence votes.

Unlike other sciences, such as natural science (as the law of gravity) and even social science, it is impossible to empirically verify the content of laws. This is because they are normative, i.e. they state how people ought to behave or what they should require of each other, as opposed to descriptive statements, such as the facts about the world around us (like the law of gravitation).

There are many sub-categories within law. For example, employment law concerns the tripartite industrial relationship between worker, employer and trade union. Family law covers marriage, divorce and child care. Civil procedure law covers the rules courts must follow as trials and appeals proceed. Evidence law is about what materials are admissible in court. There is also a large area of public law, which includes water, energy and communications regulation. This area is particularly complex because of the role of private companies in managing these services and the fact that they are bound to varying degrees of social responsibility, which are encoded in law. In addition, there are several branches of law which address the relationships between countries: international law; space law; and maritime law.