Law is a set of rules that a society or government develops to deal with issues such as crime, business agreements and social relationships. These rules are enforced by a group of people called police and courts, and they are intended to protect individuals and groups from harm or unfair treatment. A person who breaks the law may be punished by being fined or sent to prison.

The laws of a country are usually written and voted on by a group of politicians in a legislature, such as a parliament or congress. The constitution of a country sets out the overall framework of the law, while individual laws cover specific matters of detail. The rules of law are usually divided into two main categories: procedural and substantive. Procedural laws, such as those relating to the courts, specify how trials or appeals should be conducted; substantive laws, such as those governing contracts or property, concern the rights and duties of people in society.

Countries use different systems of law, depending on their culture and history. Some, such as the United States, have a common law system, in which judges make decisions based on previous cases. Others, such as Japan, have a civil law system in which the law is laid down in codes that judges must follow when deciding cases.

There are also differences between legal subjects: for example, property law covers ownership and possession of land or other real estate, including the right in rem, which relates to specific pieces of land, versus a right in personam, which applies to everything else; intellectual property law, covering copyrights, trademarks and patents; and commercial law, which deals with companies, trusts and business transactions. Family law, labour law and criminal law are other subjects.

Some laws are based on religious beliefs or books, such as Jewish Halakhah, Islamic Shari’ah and Christian Canon law. There is also international law, which covers trade and military action between different nations, as well as treaties such as the Geneva Conventions on the conduct of war.

The function of law varies from place to place, because the political and social conditions are different. In general, however, the main functions of the law are to establish standards and maintain order, resolve disputes and protect liberties and rights. People who have enough political power can impose laws on their societies, and the law can be used to punish people who disobey it. In more authoritarian societies, laws are enforced by a government with control over the military, security services and police. In more democratic societies, the police and courts enforce the law.