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. Thus it resembles another of Balzac's greatest novels, La Rabouilleuse (The Black Sheep, 1842), in that it is set partly in Paris and partly in the provinces.

It is, however, unique among the novels and short stories of La Comédie humaine (The Human Comedy, 1799–1850) by virtue of the even-handedness with which it treats both geographical dimensions of French social life.