This paper addresses the ways in which the problem of biological individuality is posed in the work of Georges Canguilhem.In his early work,Canguilhem argued that biology must regard individuality as an absolute centre,but also argued that individuality was no more than a term within a relationship whose other term was environment. The paper considers the ways in which this tension is worked out in Canguilhem's later writings,in relation to the theory of natural selection,in the theses on the nature of norms and health for living individuals, and in relation to molecular biology and the idea of the code.The paper concludes by arguing for the centrality of philosophy to inventive scientific thought.