Given the specific subject implied by the title of this paper, a moment's thought will indicate that there are three different fields for enquiry. The first is: what form of liturgy was Theodore familiar with before his consecration to Canterbury? The second is: what liturgy did he find in Britain when he arrived? The third is: did he make any modifications to what he found? For the second and third questions, the preliminary answers must be that he will have found the Roman rite in use for mass and Office, with St Benedict's variant of the Office being used by monks; and that, as he was in a sense a ‘front man’ for Hadrian (who of the two will have had the most intimate knowledge of services in Latin), he is unlikely to have contributed anything novel himself, unless he had a devotion to particular saints, and introduced their feasts into the liturgical calendar at Canterbury.

Answers to all these questions lie outside my own expertise; but for the third this is perhaps least true, and I begin with it. In the absence of any surviving calendar or martyrology from late seventh-century Canterbury, the texts which we must explore for evidence of saints' Feasts introduced to England by Theodore are the following: Bede's Martyrologium; a group of early Anglo-Saxon calendars of which the best known is the ‘Calendar of St Willibrord’; the Gelasian sacramentaries; and the Old English Martyrology.