Law is a set of rules created and enforced by a sovereign authority that form the framework for a society to function in an orderly manner. Law is a complex subject that has been the subject of many books and debates. There is no definitive answer to the question of what constitutes a law as different legal systems and individuals have very different ideas about what laws are.

Some legal systems are based on religious precepts such as the Jewish Halakha and Islamic Sharia, while Christian canon law still survives in some church communities. However, even these religious based systems require human elaboration in the form of interpretation, reasoning by analogy, and consensus building to create a comprehensive body of laws and jurisprudence.

The primary functions of a law are to keep the peace, maintain the status quo, preserve individual rights, protect minorities against majorities and allow for orderly social change. Some legal systems perform these functions better than others. An authoritarian government can keep the peace and maintain the status quo, but it may also oppress minorities or political opponents (as in Burma, Zimbabwe or Iraq under Saddam Hussein). In contrast, an ideal democratic government has checks on power to prevent abuses of power by those in power and ensure that a new leadership takes over when old policies fail (as in the United States, France or Germany).

The complexity of law makes it a rich source of scholarly inquiry into areas such as history, philosophy, economic analysis and sociology. It raises many issues of ethics and fairness that are not easily resolved. The study of law is therefore both an academic and practical endeavour that affects the lives of millions of people around the world on a daily basis.

There are three broad categories that law is studied in, though the subjects often overlap:

Criminal law is a discipline that studies the rules and consequences of behaviour that is considered harmful to social order for moral, ethical or religious reasons. Civil law studies the rules that govern litigation between individuals or entities. Competition law, which evolved out of Roman decrees against price fixing and English restraint of trade laws at the turn of the 20th century, is now used to control businesses that might use their power to distort market prices or otherwise disadvantage consumers. Consumer law, which reflects the growing emphasis on consumer protection, includes everything from restrictions on unfair contractual terms to directives on airline baggage insurance. Regulatory law covers the management of public utilities and services such as water, energy and telecommunications. It includes issues of environmental responsibility, corporate governance and transparency. There are only a few living cultures that have a legal system based on non-modern scientific concepts, but one of them (the Inuit) is the subject of a fascinating anthropological study.8