Lost Illusions is a 2021 French drama film directed by Xavier Giannoli, from a screenplay by Giannoli and Jacques Fieschi, based upon the first two parts of Illusions perdues (1837–43) by Honoré de Balzac. It stars Benjamin Voisin, Xavier Dolan, Vincent Lacoste, Cécile de France, Gérard Depardieu, and Jeanne Balibar.

Illusions perdues — in English, Lost Illusions — is a serial novel written by the French writer Honoré de Balzac between 1837 and 1843. It consists of three parts, starting in provincial France, thereafter moving to Paris, and finally returning to the provinces. The book resembles another of Balzac's greatest novels, La Rabouilleuse, that is set in Paris and in the provinces. It forms part of the Scènes de la vie de province in La Comédie humaine.