In his History of the Church, Eusebius of Caesarea († approx. 340) presents the first comprehensive history of Christianity from its beginnings. In it, he devotes a great deal of attention to the subject of heresy. Which heresies did Eusebius know? How does he sketch them? Which ones does he suppress? The study affords an insight into Eusebius' methodology and follows the development of the first centuries of literature on heresy. Eusebius' conception of heresy is presented systematically, and its special features are evaluated against the background of antique historiography.