Eusebius in his Ecclesiastical History tells us that in addition to his great work Against Heresies, St Irenaeus wrote A Discourse in Demonstration of the Apostolic Preaching. This work was entirely lost sight of: no one seems ever to have quoted a word of it. But it has quite recently reappeared in an Armenian manuscript together with Books IV and V of the greater work. The Armenian translation proves to be a fairly close rendering of the original Greek… What Irenaeus undertakes in the present work is to set out the main points of this Apostolic message, which, as he has explained in his greater work, has been handed down in the Church by the successions of the bishops and is the same in substance in all parts of the world, and to demonstrate its truth more especially from the sacred scriptures of the Old Testament.