Law is the language that society uses to define relationships and explain rights, duties and obligations. It is a highly complex subject with subtleties and structures that cannot be easily absorbed by robots, which is why humans study it for years.

The main functions of law are to establish standards, maintain order, resolve disputes and protect liberties and rights. It is also used as a tool for social change; for example, laws made slavery and apartheid illegal.

Legal systems vary widely, as do the people and groups that create them. The most stable societies have well-defined rules and institutions to enforce them. The people that control these institutions are a major factor in determining whether or not they serve their principal functions. Those with political power tend to make and enforce the laws, though revolutions against established political-legal authority are a constant feature of politics throughout the world.

Laws cover every aspect of human life. Examples include labour law, which concerns the tripartite relationship between worker, employer and trade union; family law, which covers divorce proceedings and child custody; property law, which deals with ownership of land, buildings and assets; and criminal law, which is concerned with offences against public safety, civil rights and the privacy of the individual. There are also areas of law that regulate industries, such as energy, water and telecommunications, as well as those concerning the courts, such as civil procedure and evidence law.