Against Heresies (L. Adversus haereses, Gr. κατὰ αἱρέσεων), is a five-volume work written by St. Irenaeus of Lyons in the 2nd century.
Due to his assertion that Eleutherus was the current bishop of Rome, the work is usually dated c. 180. In it Irenaeus identifies and describes several schools of gnosticism and contrasts their beliefs with what he describes as catholic and orthodox Christianity. Only fragments of the original Greek text exist, but a complete copy exists in a wooden Latin translation, made shortly after its publication in Greek, and Books IV and V are also present in a literal Armenian translation.
- Schaff, Philip (2001) [c. 1885] "Introductory Note to Irenæus Against Heresies", Ante-Nicene Fathers, Volume I, Against Heresies, William B. Eerdmans Publishing Company.