帕雷托法则（英语：Pareto principle），也称为二八定律或80/20法则，此法则指在众多现象中，80%的结果取决于20%的原因，而这一法则在很多方面被广泛的应用。如80%的劳动成果取决于20%的前期努力、20%的人做了80%的工作或者20%的维基人贡献了80%的维基条目等等。但也常常被滥用、误用，例如解决一个问题符合80/20法则，因为80%的问题由20%的资源来解决。

这个法则最初是意大利经济学家维弗雷多·帕雷托在1906年对意大利20%的人口拥有80%的财产的观察而得出的，后来管理学思想家约瑟夫·朱兰和其他人把它概括为帕雷托法则。

The Pareto principle (also known as the 80–20 rule, the law of the vital few, and the principle of factor sparsity) states that, for many events, roughly 80% of the effects come from 20% of the causes. Management consultant Joseph M. Juran suggested the principle and named it after Italian economist Vilfredo Pareto, who, while at the University of Lausanne in 1896, published his first paper "Cours d'économie politique." Essentially, Pareto showed that approximately 80% of the land in Italy was owned by 20% of the population; Pareto developed the principle by observing that 20% of the peapods in his garden contained 80% of the peas.