Law is a system of rules created and enforced through social or governmental institutions to regulate behavior. It encompasses both natural and positive laws. Natural laws are principles that describe natural processes, such as gravity or the laws of thermodynamics. These are not based on human choice, but are immutable and unchanging.

In contrast, man-made laws are based on choices made by humans, or decisions made by groups of human beings, such as a political party or religious denomination. Man-made laws can be based on ethical values or moral judgments and can apply to any number of situations. Laws are enforceable through the state and may include criminal or civil penalties.

The most common legal fields are civil and criminal law. Criminal law deals with the punishment of persons who commit crimes, such as murder and rape. Civil law deals with the resolution of lawsuits between individuals or organizations. Law is also a source of scholarly inquiry into such topics as legal history, philosophy, economic analysis and sociology.

In common law systems (which comprise about 60% of the world’s legal systems), judicial decisions are explicitly acknowledged as “law” on equal footing with statutes adopted through legislative process and regulations issued by the executive branch. This is called the doctrine of precedent, or stare decisis. The idea is that a judge’s decision on a specific case should bind lower courts in similar cases, so that future judges will have the benefit of prior rulings to help them determine how to rule on future cases involving the same issues.

Civil law systems, on the other hand, place less emphasis on precedent and more on the concept of equality before the law. Their detailed rules are derived largely from Roman and canon law, sometimes supplemented or modified by local culture and custom.

The most important principle of law is the rule of law, which requires that all persons and institutions be accountable to laws that are publicly promulgated and equally enforced, fairly applied and independently adjudicated. It also requires separation of powers, participation in the decision-making process, avoidance of arbitrariness and procedural and legal transparency. This system of law is widely seen as the best way to protect individual rights and promote human dignity and prosperity.