The Eighteenth Brumaire of Louis Napoleon (German: Der 18te Brumaire des Louis Napoleon) was an essay written by Karl Marx between December 1851 and March 1852, and originally published in 1852 in Die Revolution, a German monthly magazine published in New York and established by Joseph Weydemeyer. Later English editions, such as an 1869 Hamburg edition, were entitled The Eighteenth Brumaire of Louis Bonaparte.

The essay discusses the French coup of 1851 in which Louis-Napoléon Bonaparte assumed dictatorial powers. It shows Marx in his form as a social and political historian, treating actual historical events from the viewpoint of his materialist conception of history. Along with Marx's contemporary writings on English politics, the Eighteenth Brumaire is a principal source for understanding Marx's theory of the capitalist state

The title refers to the Coup of 18 Brumaire in which Louis Bonaparte's uncle, Napoleon Bonaparte, seized power in revolutionary France (9 November 1799, or 18 Brumaire Year VIII in the French Republican Calendar).