Alain Badiou is arguably the most significant philosopher in Europe today. Badiou's seminars, given annually on major conceptual and historical topics, constitute an enormously important part of his work. They served as laboratories for his thought and public illuminations of his complex ideas yet remain little known. This book, the transcript of Badiou's year-long seminar on the psychoanalytic theory of Jacques Lacan, is the first volume of his seminars to be published in English, opening up a new and vital aspect of his thinking. In a highly original and compelling account of Lacan's theory and therapeutic practice, Badiou considers the challenge that Lacan poses to fundamental philosophical topics such as being, the subject, and truth. Badiou argues that Lacan is a singular figure of the "anti-philosopher," a series of thinkers stretching back to Saint Paul and including Kierkegaard and Nietzsche, with Lacan as the last great anti-philosopher of modernity. The book offers a forceful reading of an enigmatic yet foundational thinker and sheds light on the crucial role that Lacan plays in Badiou's own thought. This seminar, more accessible than some of Badiou's more difficult works, will be profoundly valuable for the many readers across academic disciplines, art and literature, and political activism who find his thought essential.