在英国普通法体系中，衡平法（英语：equity）是为解决判例法的缺点而设计的另一套法律系统。

衡平法缘起于古代英国，当时大部份法院均以普通法审理案件。由于普通法十分注重进程正义，很多人仅仅是因为未能符合进程，例如过了期限起诉，而得不到公正对待。于是大不列颠大法官设立一法院，以较为宽松的态度处理案件，这就是衡平法的来源。

In jurisdictions following the English common law system, Equity refers to the body of law which was developed in the English Court of Chancery and which is now administered concurrently with the common law.

For much of its history, the English common law was principally developed and administered in the central royal courts: the Court of King's Bench, the Court of Common Pleas, and the Exchequer. Equity was the name given to the law which was administered in the Court of Chancery. The Judicature Reforms in the 1870s effected a procedural fusion of the two bodies of law, ending their institutional separation. The reforms did not effect any substantive fusion, however. Judicial or academic reasoning which assumes the contrary amounts to a "fusion fallacy".