The Cyrenaic school of philosophy (named after its founder Aristippus' native city of Cyrene in North Africa) flourished in the fifth and fourth centuries BCE and whose importance was much recognized in ancient times. Ugo Zilioli's book provides the first book-length introduction to the school in English. This book begins by introducing the main figures of the Cyrenaic school beginning with Aristippus and by setting them into their historical context. Once the reader is familiar with those figures and with the genealogy of the school, the book offers an overview of ancient and modern interpretations of the Cyrenaics, to provide readers with alternative accounts of the doctrines they endorsed and of the role they played in the context of ancient thought. Finally, this book offers a reconstruction of Cyrenaic philosophy and shows how the ethical side of their speculation connected with the epistemology and ontology they endorsed and that, as a result, the Cyrenaics were able to offer a quite sophisticated philosophy. Indeed, Zilioli demonstrates that they represented, in ancient philosophy, an important and original metaphysical position and alternative to the kind of realism endorsed by Plato and Aristotle.