Cicero is one of the most important and influential thinkers within the history of Western philosophy. For the last thirty years, his reputation as a philosopher has once again been on the rise after close to a century of very low esteem. This Companion introduces readers to ‘Cicero the philosopher’ and to his philosophical writings. It provides a handy port-of-call for those interested in Cicero’s original contributions to a wide variety of topics such as epistemology, the emotions, determinism and responsibility, cosmopolitanism, republicanism, philosophical translation, dialogue, aging, friendship, and more. The international, interdisciplinary team of scholars represented in this volume highlights the historical significance and contemporary relevance of Cicero’s writings, and suggests pathways for future scholarship on Cicero’s philosophy as we move through the twenty-first century.