Law is a set of rules that are enforced by social or governmental institutions to govern human behaviour. Its precise definition has been a matter of ongoing debate, but it is generally recognised that law is a system of guidelines and principles that are designed to control the behaviour of individuals or groups and to protect the interests of society as a whole. Law may be created or enforced through a variety of mechanisms, including legislation (written laws passed by a legislature and signed into force by the monarch) and executive decrees; it can also be created or enforced through judicial decisions. Legal systems differ from country to country, and even within a single country there are many different legal traditions. However, most legal systems do share certain features based on historically accepted ideas of justice.

A central concept of law is who has the authority to create and enforce laws. Often this is a matter of political power; in the case of most nation-states, the person or group who commands military force can usually command the power to create and enforce law. However, there are often revolts against this power and attempts to achieve democratic rule and greater rights for citizens.

Once established, a system of law must deal with a great many diverse topics. Contract law regulates agreements to exchange goods, services or money; property law defines people’s rights and duties toward tangible items like land, buildings or cars, and intangible items like shares in a company or bank accounts. Labour law covers the tripartite relationship between employer, worker and trade union, and includes things like health and safety regulations and the right to strike. Environmental law is concerned with regulating the use of natural resources and the effect of business on the environment; banking and financial law is about setting standards for the amount of capital banks must hold, and regulations about best practice investment. Water law is about ensuring that everyone has access to clean drinking water.

The discipline that studies law is called jurisprudence, and the profession that deals with law is known as a lawyer or jurist. A lawyer’s job is to help clients understand the law and defend their rights in court or before government agencies. There are many different kinds of lawyers, ranging from transactional professionals who write contracts, to litigators who fight on behalf of their clients in court. Lawyers must complete a specific training programme, and earn a degree before they can practise law. This process is overseen by a governing body, such as the Bar Association in the United States or the Law Society in England and Wales. If they fail to comply with these requirements, they can be removed from the legal register and barred from practising law. However, most legal professionals do not fall foul of this rule. In fact, most of them never break the rules in the first place.