Against Heresies (Irenaeus)

Against Heresies (Ancient Greek: Ἔλεγχος καὶ ἀνατροπὴ τῆς ψευδωνύμου γνώσεως, Elenchos kai anatropē tēs pseudōnymou gnōseōs, "On the Detection and Overthrow of the So-Called Gnosis"), sometimes referred to by its Latin title Adversus Haereses, is a work of Christian theology written in Greek about the year 180 by Irenaeus, the bishop of Lugdunum (now Lyon in France).

In it, Irenaeus identifies and describes several schools of Gnosticism, as well as other schools of Christian thought, and contrasts their beliefs with proto-orthodox Christianity.

Until the discovery of the Library of Nag Hammadi in 1945, Against Heresies was the best surviving contemporary description of Gnosticism. Today, the treatise remains historically important as one of the first unambiguous attestations of the canonical gospel texts and some of the Pauline epistles. Irenaeus cites from most of the New Testament canon, as well as the noncanonical works 1 Clement and The Shepherd of Hermas; however, he makes no references to Philemon, 2 Peter, 3 John or Jude – four of the shortest epistles.

Only fragments of the original text in ancient Greek remain today, but many complete copies in Latin, the dates of writing of which remain unknown, still survive. Books IV and V exist in their entirety in a literal version in Armenian.