The life and teachings of Diogenes of Sinope, the Greek philosopher who gave rise to classical Cynicism, deserve careful consideration because of their relevance to contemporary ethical issues. The task of reconstructing the philosopher's life, however, is exceedingly difficult, because in his case, more than in those of other ancient philosophers, we must deal not only with the scarcity of reliable sources and testimonies, but also with the mountains of anecdotal and fictional accounts that are responsible for the creation of a veritable literary legend around the Cynic who once lived in a tub. This comprehensive study reconstructs his biography on the basis of classical and Arabic sources, identifies the main ideas and principles of his philosophy, and shows the application of his philosophical message for our contemporary world. It also includes an extensively annotated translation of Diogenes Laertius' Life of Diogenes of Sinope, which is our principal source of information about the philosopher.