Is the harmony of the Sirens in Plato’s Myth of Er derived from Early Pythagorean doctrine or is the doctrine, which in Iamblichus’ On the Pythagorean Way of Life, defines the harmony of the Sirens as being the tetractys and the oracle at Delphi, a Pseudo-pythagorean invention drawing upon this famous passage in Plato’s Republic? What does the harmony of the Sirens mean for the Pythagoreans and what does it mean for Plato? Does the Platonic image of the Sirens do any philosophical work within the context of the Republic? What is the connection, if any, between the Platonic and Pythagorean themes of the harmony of the Sirens, on one hand, and the song of the Sirens in Homer’s Odyssey, on the other? By investigating these and other relevant questions, Irini-Fotini Viltanioti offers, for the first time, a sustained study of the mythological rendition of the famous Pythagorean theory of the so-called “Harmony of the Spheres” in Plato’s Republic and in Iamblichus’ On the Pythagorean Way of Life. Filling this serious gap in current literature, this book is an important contribution to the field of Pythagorean and Platonic studies.