Law is the set of rules that a society or government creates and enforces to regulate behavior. Laws can be scientific, such as the law of gravity, which states that apples will fall down from a tree, or social, such as the law against murder. The precise definition of law is a matter of debate. However, most people would agree that a law is a principle or rule that can be logically proven in a court of justice. Law can be a social tool to maintain peace, preserve the status quo, and protect minorities against majorities. It can also promote social justice and provide for orderly social change. The specific functions of a particular legal system are reflected in its structure and traditions.

The laws of a society vary widely around the world and across time. Some of them are religious in origin and incorporate moral precepts. The Jewish Halakha, Islamic Sharia and Christian canon are examples of religious laws. Other laws are explicitly secular in nature. A secular law can be based on the scientific method, the physics of natural forces or the principles of logic and reason.

A modern legal system may consist of both a legislative branch and a judiciary. A legal philosophy, called jurisprudence, defines the goals of law, and influences legislators and judges in making decisions about laws and applying them to particular circumstances. Some of the guiding concepts of this theory are that the law should be clear and accessible to citizens, that it should respond to changing social needs by way of interpreting and creative jurisprudence, and that it should balance the interests of all citizens.

Almost every aspect of human life is affected by laws. The law can protect the environment, govern business, and settle disputes among people and between businesses. It can also protect the rights of children, the elderly and disabled individuals. It can even be used to punish a criminal. Depending on the laws of a country, a person who breaks the law may be fined, imprisoned, or exiled from the country.

In a democracy, the law can also be used to ensure that public institutions operate in a fair and honest manner. This can include regulating the amount of money that banks must keep in reserve, ensuring that hospitals are licensed, and enforcing standards on the quality of products that companies produce. The law can also govern the use of natural resources like water, air, and minerals. This can also affect how they are managed and who has ownership of them. In some cases, the law can even prohibit the import of certain goods that are considered dangerous to public health.