Marxists Internet Archive, also known as MIA or Marxists.org, is a non-profit online encyclopedia that hosts a multilingual library (created in 1990) of the works of communist, anarchist, and socialist writers, such as Karl Marx, Friedrich Engels, Vladimir Lenin, Leon Trotsky, Joseph Stalin, Mao Zedong, Rosa Luxemburg, Mikhail Bakunin, Peter Kropotkin, and Pierre-Joseph Proudhon, as well as that of writers of related ideologies, and even unrelated ones (for instance, Sun Tzu).

In the following years, however, a conflict developed between the volunteers working on the website and Zodiac, who retained control of the project and domain name.

As the scope of the archive expanded, Zodiac feared that the opening toward diverse currents of Marxism was a "slippery slope" toward sectarianism.

Beginning in November 2006, the Marxists Internet Archive faced a number of serious denial-of-service attacks, attempting to exploit a misconfiguration in their server's operating system.

In late April 2014, the small British publishers Lawrence & Wishart (L&W) chose to revoke their permission for their English language version of the Marx/Engels Collected Works to be reprinted in part on MIA.

[17] The author of the petition, Ammar Aziz, was quoted in Vice magazine: "You cannot privatize their writings—they are the collective property of the people they wrote for.

[16] He was quoted in the Washington D.C.–based Chronicle of Higher Education: "The professors and the historians will be able to write learned articles about what Marx said, but the general population are going to be left back in 1975 [the year when the publication of the Collected Works began]".

[23] Through 2013, a 3-disc CD/DVD volume archive (containing the material on the website) was sold, although many copies were distributed every year for free to individuals and groups in developing and underdeveloped countries.

As they put it: "If the Archive is shut down by a publishing conglomerate or the government, having this information widely dispersed around the world, essentially untraceable, with the content entirely intact, is a great thing.

In addition to distribution of its hard drive archives, in 2008 the MIA launched Marxist Internet Archive Publications, which has, As of October 2022[update], published eight titles including volumes on philosophy, social history, Soviet psychology and pedagogy, and an anthology of writings by José Carlos Mariátegui,[26] which it distributes through Erythrós Press and Media, LLC.

The markup and style of the archive varies from one section to the other, depending on the volunteers who work there, but all are built on a common basic document template.

It also includes a reference section called the "Encyclopedia of Marxism", containing definitions of Marxist terms, short biographies, and historical material.