In the history of the liturgy there is growth and progress, but no rupture. What earlier generations held as sacred, remains sacred and great for us too, and it cannot be all of a sudden entirely forbidden or even considered harmful. It behooves all of us to preserve the riches which have developed in the Church’s faith and prayer, and to give them their proper place.

Excerpts from Pope Benedict XVI’s letter Summorum Pontificum:

Our predecessor John Paul II having already considered the insistent petitions of these faithful, having listened to the views of the Cardinal Fathers of the Consistory of 22 March 2006, having reflected deeply upon all aspects of the question, invoked the Holy Spirit and trusting in the help of God, with these Apostolic Letters We establish the following:
Art. 1 The Roman Missal promulgated by Paul VI is the ordinary expression of the Lex orandi (Law of prayer) of the Catholic Church of the Latin rite. Nonetheless, the Roman Missal promulgated by St. Pius V and reissued by Bl. John XXIII is to be considered as an extraordinary expression of that same Lex orandi, and must be given due honour for its venerable and ancient usage. These two expressions of the Church’s Lex orandi will in no any way lead to a division in the Church’s Lex credendi (Law of belief). They are, in fact two usages of the one Roman rite.
It is, therefore, permissible to celebrate the Sacrifice of the Mass following the typical edition of the Roman Missal promulgated by Bl. John XXIII in 1962 and never abrogated, as an extraordinary form of the Liturgy of the Church. The conditions for the use of this Missal as laid down by earlier documents Quattuor abhinc annis and Ecclesia Dei, are substituted as follows:
Art. 2 In Masses celebrated without the people, each Catholic priest of the Latin rite, whether secular or regular, may use the Roman Missal published by Bl. Pope John XXIII in 1962, or the Roman Missal promulgated by Pope Paul VI in 1970, and may do so on any day with the exception of the Easter Triduum. For such celebrations, with either one Missal or the other, the priest has no need for permission from the Apostolic See or from his Ordinary.
Art. 3 Communities of Institutes of consecrated life and of Societies of apostolic life, of either pontifical or diocesan right, wishing to celebrate Mass in accordance with the edition of the Roman Missal promulgated in 1962, for conventual or “community” celebration in their oratories, may do so. If an individual community or an entire Institute or Society wishes to undertake such celebrations often, habitually or permanently, the decision must be taken by the Superiors Major, in accordance with the law and following their own specific decrees and statues.
Art. 4 Celebrations of Mass as mentioned above in art. 2 may – observing all the norms of law – also be attended by faithful who, of their own free will, ask to be admitted.
Art. 5 § 1 In parishes, where there is a stable group of faithful who adhere to the earlier liturgical tradition, the pastor should willingly accept their requests to celebrate the Mass according to the rite of the Roman Missal published in 1962, and ensure that the welfare of these faithful harmonises with the ordinary pastoral care of the parish, under the guidance of the bishop in accordance with canon 392, avoiding discord and favouring the unity of the whole Church.
§ 2 Celebration in accordance with the Missal of Bl. John XXIII may take place on working days; while on Sundays and feast days one such celebration may also be held.
§ 3 For faithful and priests who request it, the pastor should also allow celebrations in this extraordinary form for special circumstances such as marriages, funerals or occasional celebrations, e.g. pilgrimages.
§ 4 Priests who use the Missal of Bl. John XXIII must be qualified to do so and not juridically impeded.
§ 5 In churches that are not parish or conventual churches, it is the duty of the Rector of the church to grant the above permission.
Art. 6 In Masses celebrated in the presence of the people in accordance with the Missal of Bl. John XXIII, the readings may be given in the vernacular, using editions recognised by the Apostolic See.
Art. 7 If a group of lay faithful, as mentioned in art. 5 § 1, has not obtained satisfaction to their requests from the pastor, they should inform the diocesan bishop. The bishop is strongly requested to satisfy their wishes. If he cannot arrange for such celebration to take place, the matter should be referred to the Pontifical Commission “Ecclesia Dei”.
Art. 8 A bishop who, desirous of satisfying such requests, but who for various reasons is unable to do so, may refer the problem to the Commission “Ecclesia Dei” to obtain counsel and assistance.
Art. 9 § 1 The pastor, having attentively examined all aspects, may also grant permission to use the earlier ritual for the administration of the Sacraments of Baptism, Marriage, Penance, and the Anointing of the Sick, if the good of souls would seem to require it.
§ 2 Ordinaries are given the right to celebrate the Sacrament of Confirmation using the earlier Roman Pontifical, if the good of souls would seem to require it.
§ 2 Clerics ordained “in sacris constitutis” may use the Roman Breviary promulgated by Bl. John XXIII in 1962.
Art. 10 The ordinary of a particular place, if he feels it appropriate, may erect a personal parish in accordance with can. 518 for celebrations following the ancient form of the Roman rite, or appoint a chaplain, while observing all the norms of law.
Art. 11 The Pontifical Commission “Ecclesia Dei”, erected by John Paul II in 1988, continues to exercise its function. Said Commission will have the form, duties and norms that the Roman Pontiff wishes to assign it.
Art. 12 This Commission, apart from the powers it enjoys, will exercise the authority of the Holy See, supervising the observance and application of these dispositions.
We order that everything We have established with these Apostolic Letters issued as Motu Proprio be considered as “established and decreed”, and to be observed from 14 September of this year, Feast of the Exaltation of the Cross, whatever there may be to the contrary.
From Rome, at St. Peter’s, 7 July 2007, third year of Our Pontificate.