Michel Foucault is the author of emblematic books of the 20th century, which transcended the limits of languages and disciplines and made him one of the most cited thinkers in the field of humanities. Almost four decades after his death, his work continues to be redefined with the posthumous publication of courses and writings that show that the question “what did Michel Foucault say?” It remains open and suggests others: how do the texts he published during his lifetime relate to those published in recent years? What is the map and what updated assessment can we make of its thinking? And above all, what can his books tell us today? These are the questions that Edgardo Castro, recognized among the greatest Foucault scholars, sets out to answer in this new edition of the Introduction to Foucault, expanded and entirely revised. Thus, he introduces us to the young Foucault, the one from the years of learning in the fifties, who read the great classics of German philosophy, became interested in psychology and psychoanalysis while setting up his conceptual laboratory and outlining the problems that will never stop reconsidering. This journey, which clearly articulates the major themes – the relationship between reason and madness, between sexuality and subjectivity, between freedom and security, modern forms of normalization, the government of populations, the deployment of neoliberal governmentality –, reaches to the last courses at the Collège de France, focused on ethics and the links between discourse and truth. The result is a wonderful overview of Foucault's thought, which incorporates the most recent interpretations and includes a brief chronology of Foucault's life, the bibliography of his works, in French and Spanish, plus some reading suggestions to delve deeper into the main axes. A formidable work of synthesis, written with precision and ease, this Introduction makes accessible to the non-specialized reader an author who still speaks to our present.