Monoenergism (Greek: μονοενεργητισμός) was a notion in early medieval Christian theology, representing the belief that Christ had only one "energy" (energeia).
After the failure of Emperor Justinian I and the Second Council of Constantinople to mend the Chalcedonian schism and unify main Christian communities within the Byzantine Empire by a single Christology, similar efforts were renewed by Heraclius (610–641), who attempted to solve the schism between the Chalcedonian (also called dyophysite) party and the non-Chalcedonian miaphysite party, suggesting the compromise of monoenergism.
Monoenergism was accepted by the Patriarchs of Constantinople, Antioch, and Alexandria, as well as by the Armenians and was not clearly criticized by Pope Honorius I of Rome in his 635 epistle.
However, it was rejected by Athanasius I Gammolo and the strong opposition of Patriarch Sophronius of Jerusalem won wide support.
This led Heraclius to abandon the teaching in 638 (though still condemning dyoenergism) and to attempt to enforce instead the doctrine of monothelitism, opposed most notably by Maximus the Confessor.