Emmanuel Joseph Sieyès, usually known as the Abbé Sieyès, was a French Roman Catholic abbé, clergyman, and political writer who was the chief political theorist of the French Revolution (1789–1799); he also held offices in the governments of the French Consulate (1799–1804) and the First French Empire (1804–1815). His pamphlet What Is the Third Estate? (1789) became the political manifesto of the Revolution, which facilitated transforming the Estates-General into the National Assembly, in June 1789. He was offered and refused an office in the French Directory (1795–1799). After becoming a director in 1799, Sieyès was among the instigators of the Coup of 18 Brumaire, which installed Napoleon Bonaparte in power.

The French Revolution was a period of political and societal change in France that began with the Estates General of 1789, and ended with the coup of 18 Brumaire in November 1799 and the formation of the French Consulate. Many of its ideas are considered fundamental principles of liberal democracy, while its values and institutions remain central to modern French political discourse.