This chapter examines Michel Foucault's approach to the history of systems of thought, which relied upon a distinctive concept of discourse he defined in terms of rules governing the production of statements in a given empirical field at a given time. The study of these rules formed the basis of Foucault's archaeology of knowledge. The chapter first considers Foucault's conception of philosophy as the critique of the present before explaining how his criticism combined archaeological and genealogical methods of writing history and operated along three distinct methodological axes corresponding to knowledge, power, and ethics. It then describes Foucault's archaeological approach to the study of systems of thought or discourse, along with his historical approach to truth. It also discusses Foucault's theory of freedom, his views on the nature and tasks of government, and his ideas about subjectivity in relation to care for the self.