Law is the system of rules that a society creates to regulate its members and deal with crimes, business agreements, relationships and other aspects of life. In addition to its societal viewpoints that reflect on rationality, morality and order, a legal view of the world also includes coercion. It is because of this that some people argue that the ultimate definition of law is power. For example, a tyrant may issue arbitrary orders that are backed by threats. Nevertheless, this is still law because it is an expression of the power of that ruler and is therefore binding.

It is difficult to give a definitive legal definition of law because different legal systems vary in the way that they are applied. However, the prevailing view is that law comprises practices, rules and customs enacted by a sovereign as binding on its citizens. Law encompasses all areas of human life and permeates every aspect of society, influencing governance, commerce, personal relationships and individual rights. It is an essential feature of a well-run, civilised world.

The main purpose of law is to keep the peace, maintain the status quo and preserve individual rights. Some legal systems serve these purposes better than others. For example, an authoritarian government will keep the peace and preserve social stability but it may oppress minorities and political opponents (e.g., Nazi Germany and Myanmar).

Legal systems can be classified according to their source of authority: common law or statutory law. Common law is based on case law while statutory law is based on legislative rules. Some legal systems are also based on religious scripture, such as Jewish Halakha and Islamic Sharia. These are generally regarded as the supreme sources of law, although they must be further elaborated by judges through interpretation and the use of precedent.

Other important aspects of a law are torts, contract law and property law. Tort law provides compensation for those who have been wronged by others, such as in a car accident or by defamation of character. Contract law outlines the terms of commercial transactions and there are many types of contracts, each with its own set of components that must be met. Property law regulates the possession condition and rights of persons and organisations over real property and land, influencing aspects of municipal, land and family law. Other fields of law include employment law, military law and tax laws. Each of these is a highly complex area with its own specialist vocabulary and methods of application. Legal research is a broad subject area and Oxford Reference provides more than 34,000 concise definitions and in-depth, specialist encyclopedic entries on all the major subjects in the field of law. This includes criminal, business, employment, constitutional, international and family law, as well as major debates in legal theory. All of these are written by experts and designed to help researchers at all levels. This comprehensive legal dictionary is the most up-to-date and complete law resource available on the market.