In her collection of essays on the history of French political and constitutional thought since the Revolution, the author places Father Sieyes at the heart of the development of republican values in France. Father Sieyes, who is known for his pamphlet Qu’est-ce que le Tiers État? (What is the Third Estate?), is regarded as the creator of European constitutionality. Pascale Pasquino’s thesis is backed by Sieyes’s manuscripts, housed at the French Archives Nationales and published here for the first time. This is an important work by a central figure in the history of political thought.Pascale Pasquino is a researcher at the CNRS (CREA) and a visiting professor at the New York University’s School of Law.