Dyslexia is a medical condition recognized by international classifications. Yet public intervention in this area varies: it is paramedical in France but pedagogic in the United Kingdom. The purpose of this paper is to consider reading difficulties in order to study the exercise of power on a population by referring to Foucault?s concept of biopolitics through the comparison of a range of settings. Firstly, the paper shows how the implication of specific professions and their history accounts for the constitution of a paramedical or, on the contrary, a pedagogic public concern. It then studies the constitution of a biological norm of reading through the use of measurement tools drawn from psychology and the legitimization of constitutional forms of knowledge in the area.