Law is a set of rules that governs the relationships between people and among nations. It is the foundation of orderly social change and it ensures that private and public officials are held accountable to citizens. It is fundamental to the enjoyment of public services and utilities, to curbing corruption and restraining abuse of power, to protecting human rights and achieving economic and social development.

In a society such as the United States, laws can be found in every aspect of life. Some of them are broad, such as contract law, which includes everything from buying a bus ticket to trading options on a derivatives market; it also covers issues such as property and tax law. Others are specific, such as environmental law, which regulates how people use land and water. Other types of laws regulate specific industries, such as the banking sector and financial regulation. Still other areas of law cover the relationships between people, such as family and immigration law.

There are many different ways to organize the law, and how a legal system is organised can affect its effectiveness. The United States has a common law system, which relies on the decisions of judges in cases that come before them. These decisions are then compiled and become case law. This contrasts with other countries, such as Japan, which has a civil law system, which uses codes to establish the law.

The goal of a system of laws is to provide an orderly society, one that can function with minimal conflict and maximum efficiency. Even in a well-ordered society, however, disagreements may arise. The law provides a way to resolve these disputes, avoiding the bloodshed and chaos that might otherwise result from unresolved conflicts. For example, if two people claim the same piece of property, the courts can decide who owns it. The law can also protect people from discrimination and guarantee their rights to free speech, religious belief and assembly.

A legal system should be transparent and accessible to citizens, and should be based on principles such as supremacy of law, equality before the law, accountability to the law, impartiality in the application of the law, separation of powers, participation in decision-making and legal certainty and avoidance of arbitrariness. It should also include provisions for checks and balances, transparency of finances and disclosure of information to citizens.

The main functions of the law are to (1) keep peace, (2) maintain the status quo, (3) preserve individual rights and liberties, (4) promote justice and (5) allow for orderly social change. The success of a legal system is largely dependent on its political landscape, which differs widely from nation to nation. Autocratic nations that lack popular support may fail to fulfil these aims, and in some cases oppress minorities or political opponents. Similarly, democratic governments may have trouble keeping the peace in situations of domestic or international conflict. In these cases, the legitimacy of the political-legal system is called into question, and revolts against the existing regime are a frequent occurrence.