POSTCOMMUNIO. - In the Latin rite (Roman, Ambrosian, Gallican, and Mozarabic), this is the prayer said by the priest after Communion and the singing of the people’s Communio, introduced by Dominus vobiscum; it is therefore called P. (sometimes also ad Communionem) already in the so-called Gelasian books, whereas in the Gregorian it is called Ad complendum or Ad completa, that is, to complete the Holy Mass.
The P. is recited, once the sacrifice has ended, « in cornu Epistolae », no longer in the middle of the altar. Together with the Collect and the Secret (« Super Oblata » of the Gregorian), the P. is found in the most ancient texts of the Latin rite of the fifth and sixth centuries; it has the same structure as these prayers, varies according to the feasts, and links Communion with them or with the period of the ecclesiastical year. In the Latin rite the P. is not so much a thanksgiving for Communion, as in the Eastern liturgy, but rather a supplication that Communion may have its full efficacy, may be purification from sins (remedium, subsidium, munimen, medicina caelestis), a pledge of eternal life (« redemptionis nostrae pignus », « immortalitatis almonia »), and union with Christ (« inter eius membra numeramur, cuius corpori communicamus et sanguini »).