Law is a system of rules that a society or government develops to deal with crime, business agreements, and social relationships. The term can also describe a particular field of law, such as criminal or civil law, or the people who work in it, such as lawyers and judges.

The purpose of law is to establish standards, maintain order, resolve disputes and protect liberties and rights. The United States uses a common law system, in which the laws are typically derived from judicial decisions rather than statutes. These judicial decisions, which are called case law, set precedents that future courts can review to determine how a new situation should be judged. Judges typically make their decision by balancing the facts of a given case with an understanding of the current state of law. This process allows the law to evolve over time and often makes sense in the context of a specific case, but does not provide clear, bright-line rules like those contained in a statute.

Most countries have some form of legal system, either common law or statutory. Some have a codified constitution with a bill of rights, while others, such as Japan, use a civil code. Common law systems tend to have a more flexible set of rules, while statutory laws are often more restrictive and unwieldy.

Various theories of law exist, with some arguing that it is morally imperative, while others claim it is just an instrument for the enforcing of social norms. Utilitarians, such as John Austin, argue that the main function of law is to promote the greatest amount of good for the largest number of people. Those who subscribe to the concept of natural law, such as Jean-Jacques Rousseau, assert that the laws of nature and human nature are immutable and reflect a moral order of things.

There are many types of law, including criminal, business, labor, constitutional, and evidence law. Criminal law covers a variety of activities, such as murder, robbery, burglary and fraud. Civil law deals with contracts, torts and negligence. Labor law focuses on the tripartite relationship between employer, employee and trade union. Constitutional law encompasses the rights of citizens against the state, with most countries having a bill of rights and a charter of liberty. Evidence law refers to what material can be submitted to a court in order to build a case.

The study of law has numerous subfields, including legal philosophy, legal history and comparative law. Other related articles include civil law; civil rights; canon law; cannons; criminal law; law, ethics and politics; law and economics; and the history of the legal profession. For more on the relationship between law and political structures, see constitution; ideology; and political party. For more on the law as a career, see the article on law school. For more on the law as a tool for social control, see censorship; crime and punishment; and law enforcement.