Diogenes Laertius (3rd century ce) is the author of a collection of poems entitled Pammetros and of a work in ten books known as the Lives and Opinions of Eminent Philosophers. The Lives were dedicated to a woman who was an enthusiastic Platonist (Book 3, § 47 and Book 10, § 29) and whose identity is unknown. Diogenes’ collection of poems in different meters has been for the most part lost; single poems that originally belonged to Diogenes’ Pammetros were later inserted into the narrative structure of the Lives by Diogenes himself. Diogenes’ Lives, however, have survived almost intact, with the exception of the final part of Book 7. The Lives are structured as follows: the prologue (Book 1, §§ 1–21) describes the origins of philosophy; the distinction between sages and philosophers; the succession of the philosophical schools and their separation into two main branches, Ionian philosophy and Italic philosophy; and the division of philosophy into three parts—physics, ethics, and dialectics—and ten principal philosophical schools. The books’ subjects are divided into Book 1: the sages; Book 2: the Ionic school of Anaximander, Anaximenes, Anaxagoras, Socrates, and the Socratics; Book 3: Plato; Book 4: Plato’s successors in the Academy, from Speusippus to Clitomachus; Book 5: Aristotle, Theophrastus, and their successors through Demetrius of Phaleron, including Heraclides of Pontus; Book 6: Antisthenes, Diogenes, and the Cynics; Book 7: Zeno and the Stoics (the surviving text covers as far as Chrysippus, but we presume it originally included philosophers through the time of the 1st-century-ce Roman Stoic Cornutus); Book 8: the Italic school, which includes Pythagoras and the Pythagoreans, Empedocles, and Eudoxus; Book 9: the so-called sporadic philosophers (Heraclitus and Xenophanes), Parmenides, Democritus, Protagoras, Pyrrho, and Timon; and Book 10: Epicurus. Diogenes’ Lives can be considered the earliest history of Greek philosophy to have come down to us, constituting a valuable source of information about the lives and doctrines of the major representatives of ancient philosophical schools up to the 1st century ce.