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 orthodox Christianity.