ITE, MISSA EST («Go, the dismissal is made»). – The dismissal in the Roman Mass, pronounced by the celebrant (in the solemn Mass by the deacon), is attested for the first time in the Ordo of Giovanni Archicantor, from 680 (ed. C. Silva-Tarouca, G. «Archicantor» di S. Pietro a Roma e l'Ordo Romanus da lui composto, in Atti della Pont. accad. romana di archeol., Memorie, I, 1 [1923], p. 201) and in the Ordo Romanus, I, 21 (PL 78, 948). But since the word missa, instead of the classical missio, is still used in the original sense of a dismissal, specifically of the dismissal of a solemn assembly or audience, the expression I. m. e. is already found in the fourth century, that is, in the earliest period of the use of Latin in the Roman liturgy, whereas later Missa acquired another meaning (= the end of the assembly).
The dismissal was made following the ancient practice of dissolving public assemblies, solemn audiences, e.g. imperial and Byzantine ones, judicial sessions, and religious ceremonies (or at least of not leaving them before being dismissed), as Avitus of Vienne reports in 500: «In ecclesiis palatiisque sive praetoriis missa fieri pronuntiatur, cum populus ab observatione dimittitur» (Ep. 1: PL 59, 199). Tertullian already seems to allude to it when he writes (De anima, 9): «post transacta solemnia dimissa plebe». St. Augustine too (Serm. 49, 8) speaks of the missa, that is, the dismissal of the catechumens: «Post sermonem fiat missa catechumenorum, manebunt fideles». And in the Aetheriae peregrination (25, 1 and 29, 3, 5) missa is likewise found in the sense of dismissal. In the same sense Florus explains missa=dimissio (De exposit. missae, 92: PL 119, 72).
The word Ite is common to all rites, whereas missa est exists only in the Latin rite; in the others (Greek, Byzantine, Ambrosian), in pace or another similar expression follows.
Until the eleventh century I. m. e. was said at every Mass, both festal and ferial; from that century onward, according to the author of the Micrologus (PL 151, 1011), on penitential days or when other canonical hours follow, it is changed to Benedictus Domino (v.), while at Masses for the dead Reguiesca(n) in pace is used (twelfth century according to Belet: PL 202, 36: «ex sola consuetudine generali»). It was always pronounced («levita... elevata voce cantat»: Smaragdus, In Regulam s. Benedicti, 17: PL 102, 837) in a more solemn tone as early as the ninth century; today, as a rule, in the tone of the Kyrie. From the tenth century onward tropes also began to be used for I. m. e. As an announcement to the people, it is said facing the people, whereas Benedictus Domino and Reguiesca(n) in pace, as prayers, are said facing the altar, and the celebrant also recites them together with the deacon.
Before I. m. e. the celebrant greets the people with Dominus sobiscum, and they acknowledge it by responding with the religious thanksgiving Deo gratias, just as at the lessons; in the other rites, e.g. in the Ambrosian rite, the people respond In nomine Domini.