Marxian economics, or the Marxian school of economics, is a heterodox school of political economic thought. Its foundations can be traced back to Karl Marx's critique of political economy. However, unlike critics of political economy, Marxian economists tend to accept the concept of the economy prima facie.^{[clarification needed]} Marxian economics comprises several different theories and includes multiple schools of thought, which are sometimes opposed to each other; in many cases Marxian analysis is used to complement, or to supplement, other economic approaches. An example can be found in the works of Soviet economists like Lev Gatovsky, who sought to apply Marxist economic theory to the objectives, needs, and political conditions of the socialist construction in the Soviet Union, contributing to the development of Soviet political economy.

Marxian economics concerns itself variously with the analysis of crisis in capitalism, the role and distribution of the surplus product and surplus value in various types of economic systems, the nature and origin of economic value, the impact of class and class struggle on economic and political processes, and the process of economic evolution.

Marxian economics—particularly in academia—is distinguished from Marxism as a political ideology, as well as from the normative aspects of Marxist thought: this reflects the view that Marx's original approach to understanding economics and economic development is intellectually independent from his own advocacy of revolutionary socialism. Marxian economists do not lean entirely upon the works of Marx and other widely known Marxists, but draw from a range of Marxist and non-Marxist sources.

Considered a heterodox school, the Marxian school has been criticized by claims relating to inconsistency, failed predictions, and scrutiny of nominally communist countries' economic planning in the 20th century. According to economists such as George Stigler and Robert Solow, Marxist economics are not relevant to modern economics, having "virtually no impact" and only "represent[ing] a small minority of modern economists". However, some ideas of the Marxian school have contributed to mainstream understanding of the global economy. Certain concepts developed in Marxian economics, especially those related to capital accumulation and the business cycle, have been fitted for use in capitalist systems; one such example is Joseph Schumpeter's notion of creative destruction.

Marx's magnum opus on critique of political economy was Das Kapital (Capital: A Critique of Political Economy) in three volumes, of which only the first volume was published in his lifetime (1867); the others were published by Friedrich Engels from Marx's notes. One of Marx's early works, Critique of Political Economy, was mostly incorporated into Das Kapital, especially the beginning of volume 1. Marx's notes made in preparation for writing Das Kapital were published in 1939 under the title Grundrisse.

Marx's critique of political economy took as its starting point the work of the best-known economists of his day, the British moral philosopher turned economist Adam Smith as well as David Ricardo.

In The Wealth of Nations (1776), Smith argued that the most important characteristic of a market economy was that it permitted a rapid growth in productive abilities. Smith claimed that a growing market stimulated a greater "division of labor" (i.e. specialization of businesses and/or workers) and in turn this led to greater productivity. Although Smith generally said little about laborers, he did note that an increased division of labor could at some point cause harm to those whose jobs became narrower and narrower as the division of labor expanded. Smith maintained that a laissez-faire economy would naturally correct itself over time.

Marx followed Smith by claiming that the most important beneficial economic consequence of capitalism was a rapid growth in productivity abilities. Marx also expanded greatly on the notion that laborers could come to harm as capitalism became more productive. Additionally, Marx noted in Theories of Surplus Value: "We see the great advance made by Adam Smith beyond the Physiocrats in the analysis of surplus-value and hence of capital. In their view, it is only one definite kind of concrete labour—agricultural labour—that creates surplus-value... But to Adam Smith, it is general social labour — no matter in what use-values it manifests itself — the mere quantity of necessary labour, which creates value. Surplus-value, whether it takes the form of profit, rent, or the secondary form of interest, is nothing but a part of this labour, appropriated by the owners of the material conditions of labour in the exchange with living labour".