The Ecthesis is a letter published in 638 CE by the Byzantine emperor Heraclius which defined monotheletism as the official imperial form of Christianity. It rejected the formula which opponents Sophronius and Maximus the Confessor had published at the synod of Cyprus.

The emperor sent this as an edict to all four metropolitan sees. It was signed by Cyrus of Alexandria and Arkadios II of Cyprus. But during 638 in Rome, Pope Honorius I who had supported monothelitism died. His successor Pope Severinus condemned the Ecthesis, ex cathedra, and so was forbidden his seat until 640.