Alain Badiou is the world's most influential living philosopher. Few contemporary thinkers display his breadth of argument and reference, or his ability to intervene in debates critical to both analytic and continental philosophy. "Alain Badiou: Key Concepts" presents an overview of and introduction to the full range of Badiou's thinking. Essays focus on the foundations of Badiou's thought, his 'key concepts' - truth, being, ontology, the subject, and conditions - and on his engagement with a range of thinkers central to his philosophy, including Plato, Descartes, Spinoza, Heidegger and Deleuze. Students new to Badiou will find this work, written by the key scholars in the field, accessible and comprehensive, while readers already familiar with Badiou will find detailed, focused and innovative discussions of Badiou's key themes, concepts and engagements.