Law is a system of rules or guidelines used to govern societies and to ensure that people behave ethically, fairly and in ways that do not harm other individuals. It typically includes a set of sanctions that can be enforced if these principles are violated. Law may be enforced by courts or police, for example. People use laws to protect themselves, their families and property, for example. Laws also serve to establish standards, maintain order, resolve disputes and protect liberties and rights. These purposes drive the development of laws.

It is not easy to give a clear definition of law, since legal systems differ and individuals have many different ideas about what constitutes law. Nevertheless, there are a few fundamental concepts that are common to most theories of law:

In modern legal systems, lawyers are professionals who study and argue the laws in their jurisdictions. They are called attorneys, solicitors or barristers. Lawyers may be transactional (writing contracts, for example) or litigious (going to court).

Some laws are framed by legislatures or agencies, but most laws are framed by judges in a trial-like proceeding called a case. The process of deciding a case usually involves ascertaining the facts, reading any relevant statutes or cases, and then locating precedential decisions (lawyers often refer to these as “case law”). This information is then analyzed using logical reasoning and analogies, to determine how future adjudicators should decide similar cases with similar facts.

Throughout history, many laws have been written by leaders in order to regulate society and prevent abuses of power. These laws are often based on religion or religious books, for example the Jewish Halakha, Islamic Sharia and Christian canon law. Other laws are based on cultural norms, for example the law of the land, which refers to land ownership and boundaries. Other important laws include copyright, which protects artistic works, such as songs and paintings; patent law, which protects inventions; and trust law, which outlines the rules that apply to money that is placed in a bank or investment account, for example a pension fund.