Capital: Critique of Political Economy by Karl Marx (German: Das Kapital. Kritik der politischen Ökonomie, also known as just Das Kapital), 1867–1883, is a foundational theoretical text in materialist philosophy, economics and politics.

Marx did not live to publish the planned second and third parts, but they were both completed from his notes and published after his death by his colleague Friedrich Engels.

In Capital Marx proposes that the motivating force of capitalism is in the exploitation of labor, whose unpaid work is the ultimate source of surplus value. The owner of the means of production is able to claim the right to this surplus value because he or she is legally protected by the ruling regime through property rights and the legally established distribution of shares which are by law only to be distributed to company owners and their board members.

The historical section shows how these rights were acquired in the first place chiefly through plunder and conquest and the activity of the merchant and "middle-man". In producing capital (produced goods), the workers continually reproduce the economic conditions by which they labour.

Capital proposes an explanation of the "laws of motion" of the capitalist economic system, from its origins to its future, by describing the dynamics of the accumulation of capital, the growth of wage labour, the transformation of the workplace, the concentration of capital, commercial competition, the banking system, the decline of the profit rate, land-rents, et cetera.

At the time of his death (1883), Marx had prepared the manuscript for Das Kapital, Volume IV, a critical history of theories of surplus value of his time, the 19th century, based on the earlier manuscript Theories of Surplus Value (1862–63). The philosopher Karl Kautsky (1854–1938) published a partial edition of Marx's surplus-value critique and later published a full, three-volume edition as Theorien über den Mehrwert (Theories of Surplus Value) (1905–1910).