Capital: A Critique of Political Economy, also known as Capital, is a foundational theoretical text in materialist philosophy and critique of political economy written by Karl Marx, published as three volumes in 1867, 1885, and 1894. The culmination of his life's work, the text contains Marx's analysis of capitalism, to which he sought to apply his theory of historical materialism "to lay bare the economic law of motion of modern society", following from classical political economists such as Adam Smith and David Ricardo. The text's second and third volumes were completed from Marx's notes after his death and published by his colleague Friedrich Engels. Das Kapital is the most cited book in the social sciences published before 1950.

Friedrich Engels was a German philosopher, political theorist, historian, journalist, and revolutionary socialist. He was also a businessman and Karl Marx's closest friend and collaborator.