This new critical text of the philosophical part of Philodemus' On Piety (shown to be the first and not as previously thought the second), together with an English translation and full commentary, introduces a new method of reconstructing the papyrus rolls excavated from the Villa of the Papyri at Herculaneum. This new edition reveals a text that expounds Epicurus' theory of the gods and religious cult practices as an outgrowth of cultural history, and provides details of Epicurean theology, cult practices and organization of Epicurean groups, accusations of impiety among philosophers, and the philosophical criticism of mythological poetry. An innovative format presents on facing pages the technical details of the papyrus and a continuous text with running English translation, to which are attached brief explanatory notes. There is an Introduction on Epicurus and Greek religion, which explains the significance of the text for our understanding of Hellenistic philosophy and intellectual history, as well as dealing with the transmission of the text, the reconstruction of its argument, its genre, theme, and the style and syntax of Philodemus' Greek. The commentary brings new work on ancient religion and philosophy and the history of atheism to bear on the interpretation of the text.