Emmanuel Joseph Sieyès (3 March 1748 – 20 June 1836), most commonly known as the Abbé Sieyès, is a French Roman Catholic abbé, clergyman and political writer.

He is one of the chief political theorists of the French Revolution, and also plays a prominent role in the French Consulate and First French Empire.

His 1789 pamphlet What is the Third Estate?

becomes the manifesto of the Revolution, helping to transform the Estates-General into the National Assembly in June 1789.

In 1799, he is the instigator of the coup d'état of 18 Brumaire (9 November 1799), which brings Napoleon Bonaparte to power.

He also coins the term "sociologie" (French for "sociology") in an unpublished manuscript, and makes significant theoretical contributions to the nascent social sciences.