This lightly modified version of the editor’s introduction to Être marxiste en philosophie situates that 1976 text with respect to the aleatory materialism or materialism of the encounter that Althusser began to elaborate in the late 1950s; the theory of class dictatorship that he consistently took to be central to Marxism; and the deconstructive anti-philosophy that he espoused in the 1950s and again from his anti-theoreticist turn of 1966–67 on. The central stake of this turn was the elaboration of a theory of Marxist non-philosophy compatible with a materialism of the encounter: Althusser grounds it, in Être marxiste, on the concept of the “non-state” at the core of the concept of the dictatorship of the proletariat—unsurprisingly, because his understanding of the way a class dictatorship crystallizes (or fails to) out of the destruction of another doubtless provided the starting point for his elaboration of the materialism of the encounter. Whence a conceptualization of philosophy as an encounter—the encounter of class struggle—at the level of theory. Whence also a redefinition of the stakes of theoretical class struggle, of which the only significant record is Althusser’s newly published work of the mid-1970s, aside from an inconspicuous footnote in Reply to John Lewis. If Althusser had previously located the primary objective of philosophical-political battle in the social destiny of the sciences, he now broadens it to take in the destiny of all the social practices and the corresponding ideologies, whose domestication in the interests of the exploiting classes or liberation in the interests of the exploited is, he now says, what philosophical argument is ultimately about. “A Marxist in Philosophy” proposes to show how, in the mid-1970s, these elements gelled in a new configuration that gave rise to Althusser’s well-known aleatory-materialist writings of the mid-1980s.