General Instruction of the Roman Missal: Chapter IV, The Different Forms of Celebrating Mass
A Bishop blesses the people with the appropriate formula, making the Sign of the Cross three times over the people.[99]
168Immediately after the blessing, with hands joined, the priest adds, Ite, missa est (The Mass is ended, go in peace), and all answer, Deo gratias (Thanks be to God).
169Then, as a rule, the priest venerates the altar with a kiss and, after making a profound bow with the lay ministers, departs with them.
170If, however, another liturgical action follows the Mass, the concluding rites, that is, the greeting, the blessing, and the dismissal, are omitted.
B. Mass with a Deacon
171When he is present at the Eucharistic Celebration, a deacon should exercise his ministry, wearing sacred vestments. For the deacon:
Assists the priest and remains at his side;
Ministers at the altar, with the chalice as well as the book;
Proclaims the Gospel and, at the direction of the priest celebrant, may preach the homily (cf. no. 66);
Guides the faithful by appropriate introductions and explanations, and announces the intentions of the Prayer of the Faithful;
Assists the priest celebrant in distributing Communion, and purifies and arranges the sacred vessels;
As needed, fulfills the duties of other ministers himself if none of them is present.
172Carrying the Book of the Gospels slightly elevated, the deacon precedes the priest as he approaches the altar or else walks at the priest’s side.
173When he reaches the altar, if he is carrying the Book of the Gospels, he omits the sign of reverence and goes up to the altar. It is particularly appropriate that he should place the Book of the Gospels on the altar, after which, together with the priest, he venerates the altar with a kiss.
If, however, he is not carrying the Book of the Gospels, he makes a profound bow to the altar with the priest in the customary way and with him venerates the altar with a kiss.
Lastly, if incense is used, he assists the priest in putting some into the thurible and in incensing the cross and the altar.
174After the incensation of the altar, he goes to the chair together with the priest, takes his place there at the side of the priest and assists him as necessary.
175If incense is used, the deacon assists the priest when he puts incense in the thurible during the singing of the Alleluia or other chant. Then he makes a profound bow before the priest and asks for the blessing, saying in a low voice, Iube, domine, benedicere (Father, give me your blessing). The priest blesses him, saying, Dominus sit in corde tuo (The Lord be in your heart). The deacon signs himself with the Sign of the Cross and responds, Amen. Having bowed to the altar, he then takes up the Book of the Gospels which was placed upon it. He proceeds to the ambo, carrying the book slightly elevated. He is preceded by a thurifer, carrying a thurible with smoking incense, and by servers with lighted candles. There the deacon, with hands joined, greets the people, saying, Dominus vobiscum (The Lord be with you). Then, at the words Lectio sancti Evangelii (A reading from the holy Gospel), he signs the book with his thumb and, afterwards, himself on his forehead, mouth, and breast. He incenses the book and proclaims the Gospel reading. When the reading is concluded, he says the acclamation Verbum Domini (The Gospel of the Lord), and all respond, Laus tibi, Christe (Praise to you, Lord Jesus Christ). He then venerates the book with a kiss, saying privately, Per evangelica dicta (May the words of the Gospel), and returns to the priest’s side.
When the deacon is assisting the Bishop, he carries the book to him to be kissed, or else kisses it himself, saying quietly, Per evangelica dicta (May the words of the Gospel). In more solemn celebrations, as the occasion suggests, a Bishop may impart a blessing to the people with the Book of the Gospels.
Lastly, the deacon may carry the Book of the Gospels to the credence table or to another appropriate and dignified place.
176If, in addition, there is no other suitable lector present, the deacon should proclaim the other readings as well.
177After the introduction by the priest it is the deacon himself who normally announces the intentions of the Prayer of the Faithful, from the ambo.
178After the Prayer of the Faithful, while the priest remains at the chair, the deacon prepares the altar, assisted by the acolyte, but it is the deacon’s place to take care of the sacred vessels himself. He also assists the priest in receiving the people’s gifts. Next, he hands the priest the paten with the bread to be consecrated, pours wine and a little water into the chalice, saying quietly, Per huius aquae (By the mystery of this water), and after this presents the chalice to the priest. He may also carry out the preparation of the chalice at the credence table. If incense is used, the deacon assists the priest during the incensation of the gifts, the cross, and the altar; afterwards, the deacon himself or the acolyte incenses the priest and the people.
179During the Eucharistic Prayer, the deacon stands near the priest but slightly behind him, so that when needed he may assist the priest with the chalice or the Missal.
From the epiclesis until the priest shows the chalice, the deacon normally remains kneeling. If several deacons are present, one of them may place incense in the thurible for the consecration and incense the host and the chalice as they are shown to the people.
180At the final doxology of the Eucharistic Prayer, the deacon stands next to the priest, holding the chalice elevated while the priest elevates the paten with the host, until the people have responded with the acclamation, Amen.
181After the priest has said the prayer at the Rite of Peace and the greeting Pax Domini sit semper vobiscum (The peace of the Lord be with you always) and the people have responded, Et cum spiritu tuo (And also with you), the deacon, if it is appropriate, invites all to exchange the sign of peace. He faces the people and, with hands joined, says, Offerte vobis pacem (Let us offer each other the sign of peace). Then he himself receives the sign of peace from the priest and may offer it to those other ministers who are closer to him.
182After the priest’s Communion, the deacon receives Communion under both kinds from the priest himself and then assists the priest in distributing Communion to the people. If Communion is given under both kinds, the deacon himself administers the chalice to the communicants; and, when the distribution is completed, he immediately and reverently consumes at the altar all of the Blood of Christ that remains, assisted if necessary by other deacons and priests.
183When the distribution of Communion is completed, the deacon returns to the altar with the priest and collects the fragments, if any remain, and then carries the chalice and other sacred vessels to the credence table, where he purifies them and arranges them in the usual way while the priest returns to the chair. It is also permissible to leave the vessels that need to be purified, suitably covered, at the credence table on a corporal, and to purify them immediately after Mass following the dismissal of the people.
184Once the prayer after Communion has been said, the deacon makes brief announcements to the people, if indeed any need to be made, unless the priest prefers to do this himself.
185If a prayer over the people or a solemn formula for the blessing is used, the deacon says, Inclinate vos ad benedictionem (Bow your heads and pray for God’s blessing). After the priest’s blessing, the deacon, with hands joined and facing the people, dismisses them, saying, Ite, missa est (The Mass is ended, go in peace).
186Then, together with the priest, the deacon venerates the altar with a kiss, makes a profound bow, and departs in a manner similar to the procession beforehand.