Law is a set of rules that are created and enforced by social or governmental institutions to regulate behaviour. It has been variously described as a science and as an art of justice. Law governs areas of human life such as property, contract and criminal behaviour. It also provides a source of scholarly inquiry into legal history, philosophy, economic analysis and sociology.

Law has four principal purposes: establishing standards, maintaining order, resolving disputes and protecting liberties and rights. Legal systems vary widely. Some are primarily legislative, while others use a combination of laws and judicial decisions. In all, the law must be clear, publicized and stable, and should be applied evenly. It must protect individuals and their property, promote the free flow of commerce, and ensure equal access to justice. It must reflect the makeup of society and be administered by representatives and neutrals who are accessible, qualified and unbiased.

The practice of law is regulated in most countries. Lawyers are typically required to have a degree and pass a rigorous examination before being admitted to the profession. They may be known as solicitors, barristers or advocates depending on the jurisdiction. The profession is often divided into specialist areas, such as commercial law, criminal law or family law. The highest level of qualification is called a Doctor of Laws (JD).

There are many kinds of law, covering everything from property to taxation. Some laws are based on religion; the Jewish Halakha and Islamic Sharia act as guides to behavior and contain many precepts that can be interpreted through a process of Qiyas, Ijma and precedent. Other laws are based on empirical observations of human behaviour. A common example is road traffic law, which is based on observation of how people behave on the roads and the consequences of their actions.

Law is a complex subject, with many aspects that are not fully understood. In addition to establishing and enforcing standards, the legal system must be able to respond to changes in society. The development of new technologies, for example, creates challenges for legislators. The growth of the private sector also affects the law; utilities such as gas, water and telecommunications are now commonly provided by private companies, which are bound by various degrees of legal responsibility for their provision. There is a constant debate about how much the law should allow for innovation and change, or whether it should be rigidly adhered to. There are also debates about the relationship between the law and religion, as well as the relationship between the government and the law. The question of whether the law should be seen as a tool for economic development or as a way to promote civil rights is a major one for policymakers. A further issue is the increasing globalization of law. This raises concerns about the potential for different legal systems to become incompatible, and about the need for international co-operation to resolve problems that cannot be solved nationally.