The literature on Foucault has repeatedly highlighted the import role that the concept of practices play in Foucault’s conceptual framework. Yet reading Foucault’s works as analyses of practices along the three axes of knowledge, power and self-relations is not as easy as it sounds: for in order not to contradict Foucault’s analyses on the three axes, the concept of practices must fullfill a number of highly demanding conceptual conditions. I develop these in detail before I sketch an appropriate concept of practices, making use of Joseph Rouse’s work in the philosophy of science. In a third step I examine the political and theoretical implications of this reading of Foucault.