Whenever the Church has been engaged in the regulation and reformation of the
celebration of the sacred mysteries, it has always taken care that the rites themselves
should also manifest to best advantage the inexhaustible riches of Christ which they
contain and which they communicate to those who are well disposed, thus facilitating their
impregnation of the souls and lives of the faithful who take part in them.
When it is the celebration of the Eucharist which is in question, however, the Church
is particularly attentive to this point. It arranges and regulates the different forms of
eucharistic celebration to the end that they might express the various aspects of the
sacrifice of the Eucharist and impress them on the faithful.
In every type of Mass, no matter how simple, all the qualities and properties are to be
found which, of their very nature, necessarily form part of the holy sacrifice of the
Mass. Among them, however, the following are particularly to be noted:
In the first place, the unity of the sacrifice of the cross: inasmuch as a multiplicity
of Masses represent but the one and only sacrifice of Christ  and owe their sacrificial character to the fact that
they are a memorial of the bloody immolation accomplished on the cross, whose fruits are
received through this unbloody immolation.
Secondly, the unity of the priesthood: the priests who celebrate Mass are indeed many,
but they are but ministers of Christ, who exercises his priesthood through them and, to
this end, makes each of them a sharer in a very special way in his own priesthood by means
of the sacrament of Orders. It follows that when, singly, they offer the sacrifice, all of
them do so by the power of the same priesthood. They act in the place (in persona . .
. agunt) of the high priest, for whom the consecration of the sacrament of his Body
and Blood is effected through the ministry of one priest as fully as through the ministry
of several. 
Lastly, the action of the entire people of God appears with greater clarity. Every Mass
is the celebration of that sacrament by which the Church lives and grows continuously  and in which its Church's own nature is especially
manifested.  For this reason it is, more than any
of the other liturgical actions,  an action of the
entire people of God, hierarchically organized, and acting hierarchically.
These three characteristics are found in every Mass, but they are more vividly apparent
in the rite by which several priests concelebrate the same Mass.
In this manner of celebrating Mass, several priests act together with one will and one
voice, by the power of the same priesthood and in the place of the high priest, together
they consecrate and offer the one sacrifice, in one sacramental act, and together they
participate in it.
Consequently, when the sacrifice is thus celebrated, the faithful are taking an active
part, aware of what they are doing, and as befits a community, the principal manifestation
of the Church is realized  - especially if the
bishop is presiding - in unity of sacrifice and priesthood, in one sole act of
thanksgiving, around one sole altar, with ministers and holy people.
Thus it is that the rite of concelebration expresses and inculcates vividly truths of
great moment for the spiritual and pastoral lives of priests and the Christian formation
of the faithful.
For these reasons, much more than for merely practical considerations, concelebration
of the mystery of the Eucharist has existed in the Church from antiquity, in different
forms, and has survived to our own day, evolving differently, in both Easts and West.
It was for these same reasons that liturgical experts had been pursuing researches into
the matter, submitting requests that permission for concelebration be extended and that
the rite be reformed.
Finally, the Second Vatican Council, having considered the matter carefully, had
extended the faculty of concelebration to a number of cases and had ordered the
preparation of a new rite of concelebration, to be inserted into the Pontifical and the
Roman Missal.  Consequently, after he had solemnly
approved and proclaimed the Constitution on Sacred Liturgy, His Holiness Pope Paul VI
commissioned the Consilium charged with the implementation of the constitution to prepare
a rite of concelebration as soon as possible. While the rite was being prepared, it was
several times examined by the members and consultors of the Concilium and was considerably
revised. Finally, the Consilium unanimously ratified it on 19 June 1964, ordaining that,
if the Holy Father approved, it should be experimented with in different parts of the
world and in varying circumstances before being definitively approved.
The Consilium for the Implementation of the Constitution on the Sacred Liturgy, in
accordance with the wishes of the council, also prepared a rite for the
administration of Communion under both species and it defined the occasions and the manner
in which clergy, religious and laity may receive the Eucharist under both species.
For some months a number of experiments were carried out, with excellent results, with
regard to the rites both of concelebration and of Communion under both species, all over
the world. When the secretary had received reports and comments on these experiments, both
rites were submitted to a final revision in the light of the experience gained and were
submitted to the Holy Father by Cardinal Giacomo Lercaro, President of the Consilium.
The Holy Father considered the two rites very carefully, with the assistance both of
the Consilium and the Sacred Congregation of Rites, and he approved and confirmed them, speciali
modo, in their entirety and in all parts, in virtue of his authority, in an audience
with Cardinal Arcadio Maria Larraona, Prefect of the Sacred Congregation of Rites. He
ordered it to be published and to be observed by everybody from Holy Thursday, 16 April,
1965, and to be accurately transcribed into the Pontifical and Missal.