Law is a set of rules that defines the rights, duties and obligations of a person or community. There are many forms of law and they can vary by time, place and culture. Some laws are written, while others are oral. Law can be used to solve disputes or to punish a person who violates the law.

Legal systems vary greatly in their structure and substance, from strict codes to loosely defined common law. Legal systems are also classified according to the level of authority they exercise, from the centralized control of national governments to the autonomy of the family court or the local bar association.

The basic purposes of law are to set standards, maintain order, resolve disputes and protect liberties and rights. In addition, law helps to organize society and guide the economy.

In societies without a central authority, the law can be established through individual custom and tradition or by local judges and arbitrators. In modern times, laws are largely made by legislative assemblies, but judges still play an important role in interpreting and applying law.

A person who violates a law is subject to civil or criminal punishment. Civil law covers such matters as contracts, property and torts (injuries caused by negligence or wrongful acts). Criminal laws cover such violations as murder, robbery, theft and fraud.

Most societies today have some form of a central government that sets the broad policy guidelines for their citizens and establishes a code of conduct for judges. The United Nations charter calls on the Organization to assist countries in the progressive development and codification of international law, as well as to promote peaceful settlement of international disputes.

In some societies, such as the Inuit people, the law is based on oral traditions passed down through generations. Other cultures, like the ancient Egyptians and Romans, developed highly detailed laws that were adapted to new social conditions. The resulting codes of laws became the foundation for later legal systems, such as the Napoleonic law or the Germanic code.

The laws of some societies may be influenced by the beliefs and customs of religions, particularly Islam and Judaism. In such cases, religious law may be used in settling secular disputes or even as a replacement for legal system in some areas.

From a methodological standpoint, the study of law is unique among other disciplines. Unlike other sciences or social sciences, normative statements in law do not have a descriptive or causal character (such as a law of gravity). Instead, they are probabilistic in nature and based on expectations of future outcomes. This is a major difference from empirical science or even social science, where the aim is to provide accurate predictions. This ontological perspective makes the study of law particularly challenging. It is a field that requires extensive research and development of methodologies to test claims about the nature of law. Fortunately, this is being done. For example, an empiricism that uses benefit-cost analysis as a means of determining the effectiveness of laws is being applied to the field of law.