Law is a system of rules that are enforced by a government to ensure that citizens obey the rules and to ensure justice is served in cases where the rules are broken. It is the focus of much scholarly inquiry, including legal history, philosophy and sociology. Law is also a key area of research in many fields, including economic analysis and political science.

Law can be a complex subject to define. It is not as straightforward as saying “a set of rules that are created and enforceable by social or governmental institutions to regulate behavior,” because it has a normative, prescriptive character: laws tell people how they ought to behave, and what they may and must not require from others, and the consequences of behaving in certain ways. This distinguishes it from empirical science (such as the law of gravity) and even social sciences (such as the law of supply and demand in economics).

The term can refer to a particular legal field, such as criminal or civil law, or it can be used more broadly to mean all of the laws of a nation. In the latter case, the laws are usually classified into three categories for convenience:

Civil law includes fields such as family, property and commercial law. It deals with disputes between individuals, such as divorce or the sale of a house. Criminal law, on the other hand, deals with conduct that is considered harmful to society as a whole, such as stealing or murder. The punishment for such crimes is typically imprisonment or a fine.

As a rule, these laws are created by legislative bodies, interpreted by judges and enforced by law enforcement agencies. Historically, different countries have developed various legal systems, with some relying on customary law and tradition and others developing more formal legal code. For example, Roman law was heavily influenced by Greek philosophy and underwent major codification during the rule of Theodosius II and Justinian I. In contrast, British common law evolved through judicial decisions.

The judicial system tries to adhere to the principles of objectivity, with judges seeking to apply the law as objectively as possible. However, in practice, this goal is often difficult to achieve due to the fact that human beings are fallible and that it is impossible to create a law that will satisfy every person.

Other areas of law include a variety of public policy and administrative matters. These include labour law, which involves the regulation of a tripartite industrial relationship between employer, employee and trade union; space law, which addresses international law concerning activities in Earth orbit and outer space; and evidence law, which defines which materials are admissible in courts for a case to be built. All of these areas are crucial to maintaining a rule of law. This principle requires that citizens are subject to laws that are publicly promulgated, equally enforced and independently adjudicated. It also requires that citizens have a right to a fair trial and hearing.