This chapter is about approaches to the history of science developed by figures associated with the structuralist movement. It focuses on the work of Louis Althusser, and in particular his argument that Marx had played a central role in the history of science. The chapter discusses how Althusser’s ideas on this topic differed from Lacan’s own. It begins with a broad intellectual history of the structuralist movement, emphasising how structuralists struggled to theorise the process of historical change. Althusser, the chapter describes, attempted to resolve this problem, by taking from Spinoza an acausal logic of the ‘symptom’. Althusser applied this idea to argue that a fundamental shift in the history of science had been begun by Marx, and then continued by Freud. The chapter makes a detailed discussion of this argument, before illustrating how Lacan’s own way of understanding history was fundamentally different. The chapter aims to show that the position Lacan took on Marx in the late 1960s was a direct critical response to Althusser’s theories.