第四阶级（the fourth estate），又被称作第四权，是指在行政权、立法权、司法权之外的第四种制衡的力量。

第四阶级所指的是媒体、公众视听。源于西方“国民阶级”(estates of the realm)的概念。传统三个阶级分别是神职人员(上议院中的神职人员)、世俗议员(上议院中的其他人员)和下议院议员。该词的产生汇集多位思想家和作家的贡献，包括埃德蒙·伯克、理乍得·克莱尔(Richard Carlyle)和19世纪《泰晤士报》的领导人亨利·里夫(Henry Reeve)。里夫在1855年10月的《爱丁堡评论》(Edinburgh Review)上撰文写道：“今天新闻界已经真正成为了一个国民阶级；甚至比其他任何的阶级都更为强大”。

The Fourth Estate (or fourth power) is a societal or political force or institution whose influence is not consistently or officially recognized. "Fourth Estate" most commonly refers to the news media, especially print journalism or "the press". Thomas Carlyle attributed the origin of the term to Edmund Burke, who used it in a parliamentary debate in 1787 on the opening up of press reporting of the House of Commons of Great Britain. Earlier writers have applied the term to lawyers, to the British queens consort (acting as a free agent, independent of the king), and to the proletariat. The term makes implicit reference to the earlier division of the three Estates of the Realm.