Law is the system of rules that a society or government develops to deal with crime, business agreements, social relationships, and property. It is a complex and diverse subject, with many books and debates devoted to the topic. Law has also been variously described as a science and as the art of justice.

In the United States, laws are developed at three levels: federal, state, and local. The Constitution lays out the boundaries of federal law, which is defined by statutes enacted by Congress, treaties ratified by the Senate, regulations promulgated by the executive branch, and case law interpreted by the judiciary. State law varies greatly. In some areas, like family law, state legislation preempts all but the most minor federal statutes. In other areas, like aviation and railroads, federal legislation coexists with state law.

A legal system that is characterized by the rule of law provides the framework for peaceful societies. The law ensures that all members of a community are treated fairly and that their basic rights are protected. It also imposes punishments on those who violate the rules of the community. In some cases, the law also protects individuals from oppressive governments that are not legitimately elected.

The precise definition of law is a matter of longstanding debate. Some people believe that a law is simply any set of rules that are enforced by social or governmental institutions to regulate behavior. Others contend that a legal system should include principles such as the preservation of individual liberty, the protection of private property, and the equal treatment of all people regardless of their wealth or social standing.

While the definition of law is a complicated issue, there are some broad categories that help to define the subject:

Contract law regulates agreements to exchange goods, services, or anything else of value. It includes everything from buying a bus ticket to trading options on a derivatives market. Property law defines the rights and duties of people toward tangible properties, such as land or buildings, and intangible assets, such as stocks and shares. Tort law encompasses the entire imaginable spectrum of wrongs that people can inflict on one another, and partially overlaps with criminal law.

The rule of law is the fundamental principle that governs a nation’s legal systems. A nation that abides by the rule of law is democratic, transparent, and equitable. It is based on the principle that no individual or group should have power over another; that all citizens have a right to a fair hearing before a neutral tribunal; and that public officials must answer for their actions in a court of law. In addition, the rule of law prohibits discrimination and ensures that all people are free to pursue their own lives and fulfill their potential without interference from arbitrary government restrictions or repressive dictatorships. The rule of law is also reflected in the principles of democracy, human rights, and international humanitarian law.