This translation of Book I of Epiphanius’ Panarion was originally published in 1987 and was reprinted with a few changes in 1997. Demand for it has been sufficient to warrant a second edition, which is offered here. The opportunity has been taken to review and revise the translation, edit and expand the notes and index and add indices of references. Together with its companion volume, The Panarion of Epiphanius of Salamis, Books II and III, De Fide (1994) this is the only current version in a modern language of the Panarion in its entirety.