Equity is a particular body of law that was developed in the English Court of Chancery. Its general purpose is to provide a remedy for situations where the law is not flexible enough for the usual court system to deliver a fair resolution to a case. The concept of equity is deeply intertwined with its historical origins in the common law system used in England. However, equity is in some ways a separate system from common law: it has its own established rules and principles, and was historically administered by separate courts, called "courts of equity" or "courts of chancery".

Equity exists in domestic law, both in civil law and in common law systems, and in international law. The tradition of equity begins in antiquity with the writings of Aristotle (epieikeia) and with Roman law (aequitas). Later, in civil law systems, equity was integrated in the legal rules, while in common law systems it became an independent body of law.