The 21st Century Marxist Economics looks into Karl Marx's idea of alternative society as an alternative to Capitalism as its contradictions are intensified in the 21st century.

The collapse of socialism in 1989 seemed to mark the end of the history of Marxism, the core idea of socialism. However, at the onset of the 21st century, we began seeing aggravated contradictions of capitalism such as global economic crises and the intensification of inequality and with this, interest in Marxism as a metadiscourse to bring in radical change as a whole has revived.

Analyzing Marx's Capital and extending the outer range of Marxist economics, Professor Jeong Seongjin has been analyzing the 21st century capitalist social relations. Based on his analyses, Jeong has consistently insisted the necessity of the concretization of Post-Capitalist alternatives. In The 21st Century Marxist Economics, Jeong looks into Marx's concept of alternatives, focusing on the concept of association. He also looks for Marxist alternatives in Post-Capitalism such as the solidarity between Marxism and feminism, Marxist approach to environmental and urban problems, and Post-Capitalist conception of a participatory-planned economy.

Jeong claims that 21st century Marxist economics considers how to restore the tradition of the demolished and forgotten "Communist A, B, C" and how to incorporate and develop them into Post-Capitalist modeling and simulations. The 21st Century Marxist Economics contains his writings about these ideas and consists of two parts.

Part 1 “Marx and Marxist Revolution” includes Chapter 1 “Association and the Revolution of Marx’s Post-Capitalism,” Chapter 2 “From Lenin to Marx,” and Chapter 3 “Re-evaluation of Soviet Planned Economy Model.” In these chapters, Jeong attempts first to correct and revolutionize non-Marxist or anti-Marxist Marxisms after Marx, and then to read anew Marx’s Post-Capitalism with the concept of association. In doing so, he emphasizes that the idea of Post-Capitalism is not an unchangeable truth that is completed once and for all but an open system that is undergoing evolution.

Part 2 “Search for Post-Capitalist Alternatives” includes Chapter 4 “Solidarity between Marxism and Feminism,” Chapter 5 “Alternatives to Eco-Socialism and Urban Marxism,” and Chapter 6 “Post-Capitalist Conception of Participatory-Planned Economy.” In Part 2, Jeong involves and extends Marx’s Post-Capitalist conceptions into the areas of feminism, eco-socialism, and urban-Marxism. Here he is inviting the readers to reappraise Marx’s ideas that were thought to be outmoded and to apply those Marxist alternatives to solve problems in our time.