The On Poems by Philodemus (c. 110-35 BC), the Epicurean philosopher and poet who taught Virgil and influenced Horace, is our main source for Hellenistic literary theory. In Book 1 Philodemus summarizes a survey of previously unknown poetic and aesthetic theories. Compiled by Crates of Mallos this survey reviews the critical theories of earlier Epicureans, Peripatetics, and Stoics, who argued in some way that sound is the source of poetic excellence, and that the ear, unaided by the mind, can judge it. Philodemus led the reaction against this invasion of Hellenistic literary criticism by musical theory, arguing that form and content are interrelated, and that substantive content, not pretty sound, is what makes poetry worthwhile. The 200 fragments of Book 1 were entirely jumbled after its discovery at the site of Vesuvius' destruction of Herculaneum. This edition reconstitutes their original sequence, according to a new method, while exploiting previously unknown manuscript sources and new techniques for reading the extant pieces. In thus restoring this important aesthetic treatise from antiquity, it makes a major addition to the corpus of classical literature.