Marxism? Think one, two, many Marxes …

"All I know is that I am not a Marxist," Karl Marx is reported to have said. He made this much quoted remark with a nod to the Marxist current developing in France at the time. We do not know what exactly Marx was distancing himself from. What is certain, however, is he could not have anticipated one thing: the extent to which, following his death, in his name, though in the form of an "ism," one of the most influential intellectual currents and political movements would spread across the entire globe – Marxism.

Over time, there would emerge hundreds of understandings, ways of thinking, theoretical and political currents and factions. Distinct from one another not only in terms of intellectual/theoretical and political/practical terms, they would also assume entirely different forms geographically and spatially, and undergo ruptures and divisions in the course of their development. Due to the variety of guises "Marxism" has historically assumed, it makes more sense to speak of Marxisms in the plural – or of theory and practice "following Marx."

In spite of all this variety and complexity, the focus was consistently upon the relationship between "theory" and "practice." This relationship, however, remains unclear and controversial to this day: does theory "following Marx" not strive to be a political practice in its own right? Is it "only" the necessary precondition for practice? Or can a sensible analysis and critique of social relations only emerge within a political practice? And what might the unity of theory and practice look like, when the unity within a "revolutionary practice," which Marx himself advocated and which still seemed possible during his day and during the era of the labour movement, has broken up during the 20th century?

In spite of all the difficulties and ambiguities inherent to the relationship between theory and practice, it seems sensible to present two distinct overviews: one of "theories and debates following Marx" and one of "political organisations and movements following Marx." Such a distinction must remain schematic, and there are both connections and inevitable overlaps. Moreover, neither of the two overviews can stake a claim to being exhaustive and complete, given the diversity and the global distribution of the forms of thinking and acting that build on Marx's critique. Nevertheless, such overviews can present a first orientation and an introduction.