SACRED CONGREGATION FOR THE DOCTRINE OF THE FAITH
INSTRUCTION ON MIXED MARRIAGES*
Our Lord Jesus Christ instituted the sacrament of marriage as a symbol of His union with the Church, in order to present a fuller explanation of his sanctifying power and the model of this great mystery in the lives of the spouses (cf. Eph 5:32), who in virtue of their intimate communion of life, represent the love with which Christ offered himself for the salvation of mankind. The sacrament of marriage requires more than anything else the full and perfect harmony of the spouses themselves, especially in regards to religion: “In fact the union of spirits may fail or at least be weakened when there are differences of belief and oppositions of the will concerning religious truths and sentiments that make up the highest values that are the subject of human veneration.”  For these reasons, the Church considers it her most solemn duty to protect and safeguard the gift of the faith both for the spouses as well as their children. And for this very reason, it strives in every way so that Catholics do not enter into marriage with non-Catholics.
Obvious evidence of the Church’s attentive desire is found in the ecclesiastical discipline on mixed marriages, sanctioned in the norms of the Code of Canon Law which concretely expresses the double impediment of mixed religion and disparity of cult; the first of which prohibits marriages of Catholics with baptized non-Catholics, except for the validity of marriage,  the second of which renders null the marriage contracted by a Catholic with a non-baptized person. 
Another clear argument of the Church’s desire to preserve the sanctity of Christian marriage is found in the defined juridic form for the manifestation of consent, though there have actually been different norms in the past from time to time in this regard, always however providing that clandestine weddings were not permitted.
Guided by the same concern, all the sacred Pastors should have the same desire to teach the faithful about the importance and the excellence of this sacrament, and to admonish them about the dangers inherent in the marriage of a Catholic with a non-Catholic Christian and even more so in the marriage with a non-Christian. They should strive with all appropriate means to lead the young to contract marriage with a Catholic party.
It cannot be denied, however, that the characteristic conditions of our time, which have quickly caused radical transformations in social and family life, make the observance of the canonical discipline regarding mixed marriage even more difficult than in the past.
Indeed, in the present circumstances, the relations between Catholics and non-Catholics are much more frequent, their habits are more closely aligned, and their customs are more similar, such that friendship between them arises much more easily, leading to more frequent occasions of mixed marriage as experience has shown.
Therefore, the pastoral concern of the Church today demands more than ever that the holiness of marriage be safeguarded in conformity with Catholic doctrine and that the faith of the Catholic spouse and the Catholic education of the offspring be guaranteed, even in mixed marriages, with the greatest possible diligence and effectiveness. Such pastoral care is even more necessary because, as it has been noted, there are many opinions held by non-Catholics that are at odds with Catholic doctrine about the essential qualities and properties of marriage, in particular regarding indissolubility, and consequently divorce and a subsequent marriage after civil divorce. Thus, the Church recognizes its duty to forewarn the faithful not to run the risk of endangering their faith, either spiritually or materially. The Church therefore take every precaution to instruct those who intend to contract marriage regarding its nature, its properties, the obligations inherent in marriage itself, and the dangers to avoid.
Furthermore, it cannot be ignored in this regard that Catholics must take into account what has been solemnly defined in the Second Vatican Ecumenical Council through the Decree “de Oecumenismo,” in the course of conduct with our brethren separated from the Catholic Church. This new discipline suggests that the severity of the present legislation be attenuated with respect to mixed marriage, not in regards divine law, but in relation to the ecclesiastical norms that our separated brethren sometimes consider offensive.
It is easy to understand that such a grave problem has not at all escaped the attention of the Second Vatican Ecumenical Council, which was announced by the Supreme Pontiff John XXIII of happy memory precisely to meet the needs of the Christian people. And indeed the Council Fathers expressed various opinions on the subject, which have been rightly and carefully considered.
Therefore, after having consulted the sacred Pastors on this subject, and having attentively evaluated all the circumstances, the two impediments of mixed religion and disparity of cult will remain in force, though local Ordinaries are granted the faculty to dispense them according to the provisions of the Apostolic Letter Pastorale Munus, no. 19 and 20 when a grave cause is present, and provided that the prescriptions of the law are observed. Furthermore, the following provisions promulgated by the authority of His Holiness Pope Paul VI, and retained in the legislation proper to the Oriental Churches, will be definitively introduced in the Code of Canon Law which is currently being revised if experience shows them to be positively received.
I. - 1) The criterion should be kept in mind that it is always necessary to avoid any risk to the faith of the Catholic spouse and that the Catholic education of the children should always be diligently provided for. 
2) The local Ordinary or the pastor of the Catholic party should take care to inculcate in grave terms the obligation of providing a Catholic baptism and the Catholic education for offspring: In fulfillment of this obligation, guarantees should be required by means of the explicit promise of the Catholic spouse as a precaution.
3) The non-Catholic party, with appropriate delicacy but also in clear terms, should be informed about the Catholic doctrine regarding the dignity of marriage, and especially about its principal properties, name unity and indissolubility. The non-Catholic party should also be informed about the grave obligation for the Catholic spouse to protect, preserve, and practice his or her own faith and to baptize and educate any offspring to be born in the same faith.
Because this obligation must be guaranteed, even the non-Catholic spouse is invited to promise, openly and sincerely, that he or she will not create any obstacle to the fulfillment of this obligation. If the non-Catholic later believes that he or she cannot make this promise without harming his or her own conscience, the Ordinary should refer the case with all its elements to the Holy See.
4) Although these promises are ordinarily to be made in writing, it is nevertheless within the discretion of the Ordinary – whether as a general rule or case by case – to establish whether these promises are to be made in writing or not, whether they are to be made by the Catholic party, the non-Catholic party, or both, and also to determine if they should be recorded in the marriage documents.
II. - If it should happen, as sometimes occurs in certain regions, that the Catholic education of the children is truly impossible, not because of the wishes of the spouse but rather because of the laws and customs of the people which the parties are not able to circumvent, the local Ordinary, having considered these circumstances, can dispense from this impediment provided that the Catholic party is willing, in so far as possible, to do everything he or she can to have the children born of the marriage baptized and educated as Catholics, likewise provided that there are guarantees of the good will of the non-Catholic party.
In granting these permissions, the Church is animated also by the hope that the civil laws adverse to human liberty may be abrogated, as well as those that prohibit the Catholic education of offspring or the exercise of the Catholic faith, and that the force of natural law in these matters be recognized.
III. - In celebration of mixed marriages, canonical form must be observed according to the provisions of canon 1094 as well as that which is required for the validity of the marriage itself. If, however, there are difficulties, the Ordinary must refer the case with all its elements to the Holy See.
IV. - In regards to the liturgical form, and derogating from canons 1102 §3 and §4, and 1109 §3, local Ordinaries are granted the faculty to permit the use of sacred rites in the celebration of mixed marriages, with the customary blessing and discourse.
V. - Any simultaneous celebration in the presence of a Catholic priest and a non-Catholic minister exercising their respective rites must be absolutely avoided. Nevertheless, it is not forbidden that the non-Catholic minister address some words of encouragement or exhortation following the religious ceremony and that some of the prayers be recited in common with the non-Catholic. This provision can be adopted with the consent of the local Ordinary and with necessary precautions taken to avoid the danger of wonder.
VI. - Local Ordinaries and pastors are to attentively monitor that the families originating from mixed marriages lead a holy life in conformity with the promises made, especially regarding the instruction and Catholic education of the offspring.
VII. - The excommunication prescribed by canon 2319 §1, 1° for those who celebrate a marriage before a non-Catholic minister is abrogated. The effects of this abrogation are retroactive.
In establishing these new rules, it is the mind and the intention of the Church, as stated above, to provide for the current needs of the faithful and to promote a more fervent sense of charity in the reciprocal relationships between Catholics and non-Catholics.
Those who have the duty of teaching Catholic doctrine to the faithful, and especially pastors, are to strive with all their heart and with constant care to observe this intention. They should work toward this end with all charity and always with the respect due to others, especially non-Catholics who follow their convictions in good faith.
Thus, Catholic spouses are to take care to strengthen and grow in the gift of the faith, and while always leading a family life informed by Christian virtues, they are also to strive to offer a shining example to the non-Catholic party and children.
Given in Rome, March 18, 1966.
Cardinal Alfredo Ottaviani
+ Pietro Parente
This Instruction, having been published already on March 18, 1966, is included in the acts now promulgated and comes into force on May 19, 1966, the feast of the Ascension of Our Lord Jesus Christ.
* AAS 58 (1966), 235-239; Italian translated by L’Osservatore Romano, n. 65, March 19, 1966, pp. 1-2.
 Pius XI, Encyclical Letter Casti connubii.
 Canons 1060-1064.
 Canons 1070-1071.
 Cf. can. 1060.