How about marriage between members of different Christian denominations? Are Catholics, Protestants and Orthodox allowed to intermarry?
Answer: In its Codex Iuris Canonici (CIC) of 1983 the Law of the Roman-Catholic Church regulates the question of marriage between Christians belonging to different denominations in the canons 1124 ff.
Can. 1124 Without the express permission of the competent authority, marriage is prohibited between two baptised persons, one of whom was baptised in the Catholic Church or received into it after baptism and has not defected from it by a formal act, the other of whom belongs to a Church or ecclesial community not in full communion with the Catholic Church.
Can. 1125 The local Ordinary can grant this permission if there is a just and reasonable cause. He is not to grant it unless the following conditions are fulfilled:
1° the Catholic party is to declare that he or she is prepared to remove dangers of defecting from the faith, and is to make a sincere promise to do all in his or her power in order that all the children be baptised and brought up in the Catholic Church;
2° the other party is to be informed in good time of these promises to be made by the Catholic party, so that it is certain that he or she is truly aware of the promise and of the obligation of the Catholic party
3° both parties are to be instructed about the purposes and essential properties of marriage, which are not to be excluded by either contractant.
Can. 1126 It is for the Episcopal Conference to prescribe the manner in which these declarations and promises, which are always required, are to be made, and to determine how they are to be established in the external forum, and how the non-Catholic party is to be informed of them.
Can. 1127 §1 The provisions of can. 1108 are to be observed in regard to the form to be used in a mixed marriage. If, however, the Catholic party contracts marriage with a non-Catholic party of oriental rite, the canonical form of celebration is to be observed for lawfulness only; for validity, however, the intervention of a sacred minister is required, while observing the other requirements of law.
§2 If there are grave difficulties in the way of observing the canonical form, the local Ordinary of the Catholic party has the right to dispense from it in individual cases, having however consulted the Ordinary of the place of the celebration of the marriage; for validity, however, some public form of celebration is required. It is for the Episcopal Conference to establish norms whereby this dispensation may be granted in a uniform manner.
§3 It is forbidden to have, either before or after the canonical celebration in accordance with §1, another religious celebration of the same marriage for the purpose of giving or renewing matrimonial consent. Likewise, there is not to be a religious celebration in which the catholic assistant and a non-Catholic minister, each performing his own rite, ask for the consent of the parties.
Can. 1128 Local Ordinaries and other pastors of souls are to see to it that the Catholic spouse and the children born of a mixed marriage are not without the spiritual help needed to fulfil their obligations; they are also to assist the spouses to foster the unity of conjugal and family life.