Georges Canguilhem (1904-1995) was a renowned historian of science who argued that the practice of science implies philosophy and, thus, scientists who fail to question their philosophical principles inevitably reproduce the dominant philosophical system of their age. In opposition to the idea that science uncovers a pre-existing truth, Canguilhem asserts that scientists produce truth. Therefore, the products of scientists' labor are social constructs, reflecting the norms governing a given society. In my research project, I will be delineating the effects of Canguilhem's work on Althusser's concept of ideology as material practice rather than illusion. Using Althusser's unpublished notes on Canguilhem (located at the Althusser archives in Paris), I will explore how his relationship with Canguilhem effects the task of re-reading Althusser's central concept of ideology.