Irenaeus of Lyons.

One of the Christian heresiolists.

Attributed text(s).
Against Heresies.
Demonstration of the Apostolic Preaching (to Marcianus).
Against the Nations.
On Discipline.
On Schism (to Blastus).
Epistle to Florinus.
Commentary on the Ogdoad.
Various treatises.

Available text(s).
Tertullian Project: Proof of the Apostolic Preaching (English only).
Skeptik (Greek fragments of Against Heresies only).
On site: Epistle to Florinus (present page in Greek, English).
On site: Against Heresies (English translation with links to .jpg images of Latin and Greek by Harvey).

Books 1, 2, 3, 4, 5.
Image of papyrus Oxyrhynchus 405 (fragment of Against Heresies 3.9.3, quoting Matthew 3.16-17; refer to the notes and quotes page for more information).

Related text(s).

Useful links.
Irenaeus at EarlyChurch.
Irenaeus in the Catholic Encyclopedia.
Irenaeus at Early Christian Writings.

Irenaeus was a Christian heresiologist and presbyter of Lyons who flourished late in century II.

Tertullian, Against the Valentinians 5.1 (English translation slightly modified from that of Mark T. Riley):

Mihi autem cum archetypis erat limes principalium magistrorum, non cum affectatis ducibus passivorum discipulorum. nec undique dicemur ipsi nobis finxisse materias quas tot iam viri sanctitate et praestantia insignes, nec solum nostra antecessores sed ipsorum haeresiarcharum contemporales, instructissimis voluminibus et prodiderunt et retuderuntut Iustinus, philosophus et martyr; ut Miltiades, ecclesiarum sophista; ut Irenaeus, omnium doctrinarum curiosissimus explorator; ut Proculus noster, virginis senectae et Christianae eloquentiae dignitas, quos in omasi opere fidei quemadmodum in isto optaverim adsequi.

My exposition will be limited to the original teachings of their chief teachers; it will not include the high-flying leaders of the mass of followers. I hope no one will say because of this limitation that I have invented this material for the occasion. No indeed, many men who were renowned for their holiness and their leadership, who were not only our predecessors but also contemporaries of those very heresiarchs, have exposed and refuted them in learned volumes. I refer to Justin, philosopher and martyr, Miltiades, that churchly sage, Irenaeus, an eager discoverer of all doctrines, and our own Proculus, the living exemplar of a chaste old age and of Christian eloquence. In their footsteps I might hope to follow in all works of faith, just as I do in this work.

Hippolytus mentions Irenaeus twice in his Refutation. The first mention is in 6.37:

Και γαρ και ο μακαριος πρεσβυτερος Ειρηναιος, παρρησιαιτερον τω ελεγχω προσενεχθεις, τα τοιαυτα λουσματα και απολυτρωσεις εξεθετο, αδρομερεστερον ειπων α πρασσουσιν....

For also the blessed presbyter Irenaeus approached the topic more frankly and explained such washings and redemptions, telling in a broad sense what they practice....

The second is in 6.30 (English translation slightly modified from the ANF series translation): now the blessed presbyter Irenaeus has powerfully and elaborately refuted the opinions of these men [ηδη του μακαριου πρεσβυτερου Ειρηναιου δεινως και πεπονημενως τα δογματα αυτων διελεγξαντος]. And to him we are indebted for a knowledge of their inventions, proving that these heretics, appropriating these opinions from the Pythagorean philosophy, and from overspun theories of the astrologers, cast an imputation upon Christ, as though he had delivered these things [παρ ου και αυτων εφευρηματα επιδεικνυντες αυτους, Πυθαγορειου φιλοσοφιας και αστρολογων περιεργιας, ταυτα σφετερισαμενους εγκαλειν Χριστω, ως ταυτα παραδεδωκεναι].

Eusebius, History of the Church 5.20.4-8 (English translation slightly modified from that in the Nicene and Post-Nicene Fathers):

Εν η γε μην προειρηκαμεν προς τον Φλωρινον ο Ειρηναιος επιστολη αυθις της αμα Πολυκαρπω συνουσιας αυτου μνημονευει, λεγων·

In the epistle to Florinus, of which we have spoken, Irenaeus mentions again his intimacy with Polycarp, saying:

Ταυτα τα δογματα, Φλωρινε, ινα πεφεισμενως ειπω, ουκ εστιν υγιους γνωμης· ταυτα τα δογματα ασυμφωνα εστιν την εκκλησια εις την μεγιστην ασεβειαν περιβαλλοντα τους πειθομενους αυτοις· ταυτα τα δογματα ουδε οι εξω της εκκλησιας αιρετικοι ετολμησαν αποφηνασθαι ποτε· ταυτα τα δογματα οι προ ημων πρεσβυτεροι, οι και τοις αποστολοις συμφοιτησαντες, ου παρεδωκαν σοι.

These doctrines, Florinus, to speak mildly, are not of sound judgment. These doctrines disagree with the church and drive into the greatest impiety those who accept them. These doctrines not even the heretics outside of the church have ever dared to publish. These doctrines the presbyters who were before us and who were companions of the apostles did not deliver to you.

Ειδον γαρ σε, παις ετι ων, εν τη κατω Ασια παρα Πολυκαρπω, λαμπρως πρασσοντα εν τη βασιλικη αυλη και πειρωνμενον ευδοκιμειν παρ αυτω. μαλλον γαρ τα τοτε διαμνημονευω των εναγχος γινομενων, αι γαρ εκ παιδων μαθησεις συναυξουσαι τη ψυχη, ενουνται αυτη, ωστε με δυνασθαι ειπειν και τον τοπον εν ω καθεζομενος διελεγετο ο μακαριος Πολυκαρπος, και τας προοδους αυτου και τας εισοδους και τον χαρακτηρα του βιου και την του σωματος ιδεαν και τας διαλεξεις ας εποιειτο προς το πληθος, και την μετα Ιωαννου συναναστροφην ως απηγγελλεν και την μετα των λοιπων των εορακοτων τον κυριον, και ως απεμνημονευεν τους λογους αυτων, και περι του κυριου τινα ην α παρ εκεινων ακηκοει, και περι των δυναμεων αυτου, και περι της διδασκαλιας ως παρα των αυτοπτων της ζωης του λογου παρειληφως ο Πολυκαρπος απηγγελλεν παντα συμφωνα ταις γραφαις.

For when I was a boy I saw you in lower Asia with Polycarp, doing brilliantly in the royal court, and endeavoring to gain his approbation. I remember the events of that time more clearly than those of recent years. For what boys learn, growing with their mind, becomes joined with it, so that I am able to describe the very place in which the blessed Polycarp sat as he discoursed, and his goings out and his comings in, and the manner of his life, and his physical appearance, and his discourses to the people, and the accounts which he gave of his intercourse with John and with the others who had seen the Lord. And as he remembered their words and what he heard from them concerning the Lord, and concerning his miracles and his teaching, having received them from eyewitnesses of the word of life, Polycarp related all things in harmony with the scriptures.

Ταυτα και τοτε δια το ελεος του θεου το επ εμοι γεγονος σπουδαιως ηκουον, υπομνηματιζομενος αυτα ουκ εν χαρτη, αλλα εν τη εμη καρδια· και αει δια την χαριν του θεου γνησιως αυτα αναμαρυκωμαι, και δυναμαι διαμαρτυρασθαι εμπροσθεν του θεου οτι ει τι τοιουτον ακηκοει εκεινος ο μακαριος και αποστολικος πρεσβυτερος, ανακραξας αν κα εμφραξας τα ωτα αυτου και κατα το συνηθες αυτω ειπων· Ω καλε θεε, εις οιους με καιρους τετηρηκας, ινα τουτων ανεχωμαι, πεφευγει αν και τον τοπον εν ω καθεζομενος η εστως των τοιουτων ακηκοει λογων.

These things being told me by the mercy of God, I listened to them attentively, noting them down, not on paper, but in my heart. And continually, through the grace of God, I recall them faithfully. And I am able to bear witness before God that, if that blessed and apostolic presbyter had heard any such thing, he would have cried out and stopped his ears and, as was his custom, would have exclaimed: O good God, unto what times have you spared me that I should endure these things? And he would have fled from the place where, sitting or standing, he had heard such words.

Και εκ των επιστολων δε αυτου ων επεστειλεν ητοι ταις γειτνιωσαις εκκλησιαις, επιστηριζων αυτας, η των αδελφων τισι, νουθετων αυτους και προτρεπομενος, δυναται φανερωθηναι.

And this can be shown plainly from the epistles which he sent, either to the neighboring churches for their confirmation or to some of the brethren, admonishing and exhorting them.

Ταυτα ο Ειρηναιος.

These are the things that Irenaeus wrote.

Jerome, On Famous Men 35:

Irenaeus, Pothini episcopi, qui Lugdunensem in Gallia regebat ecclesiam, presbyter, a martyribus eiusdem loci, ob quasdam ecclesiae quaestiones legatus Romam missus, honorificas super nomine suo ad Eleutherum episcopum perfert litteras. postea iam Pothino prope nonagenario, ob Christum martyrio coronato, in locum eius substituitur. constat autem Polycarpi, cuius supra fecimus mentionem, sacerdotis et martyris, hunc fuisse discipulum. scripsit quinque adversus haereses libros, et contra gentes volumen breve, et de disciplina aliud, et ad Martianum fratrem de apostolica praedicatione, et librum variorum tractatuum, et ad Blastum de schismate, et ad Florinum de monarchia, sive quod Deus non sit conditor malorum, et de ogdoade egregium commentarium, in cuius fine significans se apostolicorum temporum vicinum fuisse, sic subscripsit: Adiuro te, qui transcribis librum istum, per dominum Iesum Christum, et per gloriosum eius adventum, quo iudicaturus est vivos et mortuos, ut conferas, postquam transcripseris, et emendes illum ad exemplar, unde scripsisti, diligentissime; hanc quoque obtestationem similiter transferas, ut invenisti in exemplari. feruntur eius et aliae ad Victorem episcopum Romanum de quaestione Paschae epistolae, in quibus commonet eum, non facile debere unitatem collegii scindere. siquidem Victor multos Asiae et Orientis episcopos, qui decima quarta luna cum Iudaeis Pascha celebrabant, damnandos crediderat. in qua sententia hi, qui discrepabant ab illis, Victori non dederunt manus. Floruit maxime sub Commodo principe, qui M. Antonino Vero in imperium successerat.

Irenaeus, a presbyter under Pothinus the bishop who ruled the church of Lyons in Gaul, being sent to Rome as legate by the martyrs of Ibis place, on account of certain ecclesiastical questions, presented to bishop Eleutherius certain letters under his own name which are worthy of honor. Afterward, when Pothinus at nearly ninety years of age received the crown of martyrdom for Christ, he was put in his place. It is certain too that he was a disciple of Polycarp, the priest and martyr, whom we mentioned above. He wrote five books against heresies and a short volume, against the nations; and another on discipline; a letter to Marcianus his brother on apostolical preaching; a book of Various treatises; also to Blastus on schism; to Florinus on monarchy or that God is not the author of evil; also an excellent commentary on the ogdoad at the end of which, indicating that he was near the apostolic period, he wrote: I adjure you, whoever shall transcribe this book, by our Lord Jesus Christ and by his glorious advent at which he shall judge the quick and the dead, that you diligently compare, after you have transcribed, and amend it according to the copy from which you have transcribed it and also that you shall similarly transcribe this adjuration as you find it in your pattern. Other works of his are in circulation, to wit, to Victor the Roman bishop On the paschal controversy, in which he warns him not lightly to break the unity of the fraternity, if indeed Victor believed that the many bishops of Asia and the east, who with the Jews celebrated the Passover, on the fourteenth day of the new moon, were to be condemned. But even those who differed from them did not support Victor in his opinion. He flourished chiefly in the reign of the emperor Commodus, who succeeded Marcus Antoninus Verus in power.

Irenaeus wrote his antiheretical work in five volumes during the episcopate of Eleutherus of Rome, as indicated by what he writes in Against Heresies 3.3.3 (Greek courtesy of Eusebius, History of the Church 5.6.4-5):

Τον δε Κλημεντα τουτον διαδεχεται Ευαρεστος και τον Ευαρεστον Αλεξανδρος. Ειθ ουτως εκτος απο των αποστολων καθισταται Ξυστος· μετα δε τουτον Τελεσφορος, οφ και ενδοξως εμαρτυρησεν· επειτα Υγινος, ειτα Πιος, μεθ ον Ανικητος· διαδεξαμενου τον Ανικητον Σωτηρος, νυν δωδεκατω τοπω τον της επισκοπης απο των αποστολων κατεχει κληρον Ελευθερος. τη αυτη ταξει και τη αυτη διδαχη* η τε απο των αποστολων εν τη εκκλησια παραδοσις και το της αληθειας κηρυγμα κατηντηκεν εις ημας.

* Perhaps a mistake for διαδοχη.

Huic autem Clementi succedit Evaristus, et Evaristo Alexander, ac deinceps sextus ab apostolis constitutus est Sixtus, et ab hoc Telesphorus, qui etiam gloriosissime martyrium fecit; ac deinceps Hyginus, post Pius, post quem Anicetus. cum autem successisset Aniceto Soter, nunc duodecimo loco episcopatum ab apostolis habet Eleutherius. hac ordinatione et successione ea quae est ab apostolis in ecclesia traditio et veritatis praeconatio pervenit usque ad nos. et est plenissima haec ostensio, unam et eandem vivificatricem fidem esse, quae en ecclesia ab apostolis usque nunc sit conservata, et tradita in veritate.

Evarestus succeeded Clement, and Alexander succeeded Evarestus. Then Xystus, the sixth from the apostles, was appointed. After him Telesphorus, who suffered martyrdom gloriously, then Hyginus, then Pius, and after him Anicetus; Soter succeeded Anicetus, and now, in the twelfth place from the apostles, Eleutherus holds the office of bishop. In the same order and succession the tradition in the church and the preaching of the truth has descended from the apostles unto us.

However, it would also appear that he sent each volume to its intended recipient as it was completed, since he writes in the preface to the third book:

Propter quod, cum sit unius operis traductio eorum et destructio in multis, misimus tibi libros, ex quibus primus quidem omnium illorum sententias continet, et consuetudines et characteres ostendit conversationis eorum; in secundo vero destructa et eversa sunt quae ab ipsis male docentur, et nudata et ostensa sunt talia qualia et sunt. in hoc autem tertio ex scripturis inferemus ostensiones, ut nihil tibi ex his quae praeceperas desit a nobis.

On which account, since their disgracing and destruction is in many ways of one work, we have sent you books, of which the first contains the opinions of all these men, and shows their customs and the character of their conversation; in the second, moreover, the bad things that are taught by them are destroyed and overthrown, and bared and shown forth for what they are. In this, however, the third, we will infer demonstrations from the scriptures, so that nothing from among those things that you have enjoined might fall short.

And in the preface to the fourth book he writes:

Nec enim possibile est alicui curare quosdam male habentes qui ignorat passionem eorum qui male valent. quapropter hi qui ante nos fuerunt, et quidem multo nobis meliores, non tamen satis potuerunt contradicere his qui sunt a Valentino, quia ignorabant regulam ipsorum, quam nos cum omni diligentia in primo libro tibi tradidimus, in quo et ostendimus doctrinam eorum recapitulationem esse omnium haeriticorum. quapropter et in secundo tamquam speculum habuimus eos totius eversionis.

For it is not possible for any one to cure anybody who is sick if he is ignorant of their suffering who are in ill health. It was on this account that those who were before us, and who were much better than us, were unable, notwithstanding, to sufficiently counter those who were from Valentinus, because they were ignorant of the rule of these men, which we have with all diligence delivered to you in the first book, in which we have also shown their doctrine to be a recapitulation of all the heretics. On this account also in the second, as if in a mirror, we have had [a glimpse of] them at their total overthrow.

The original language of composition was Greek, which, however, is no longer extant except in fragments both from Oxyrhynchus and in the church fathers. Fortunately, an ancient Latin translation is available.