Interfaith marriage in Christianity
An interfaith marriage is typically defined as a marriage between a Christian and a non-Christian. Within the sects of Christianity, this may be extended to include inter-denominational marriage.
Some Christian local churches and churches at large may forbid interfaith marriage, basing this ban on New Testament verse 2 Corinthians 6:14 and, in some cases, the Old Testament verse Deuteronomy 7:3 (see also Ezra 9–10.). Likewise, such marriages are indirectly supported by part of the Pauline privilege, in 1 Corinthians 7:12–14, with the central excerpt: "For the unbelieving husband is sanctified through his (believing) wife, and the unbelieving wife is sanctified through her believing husband." However, it is to be noted that the context of 2 Corinthians 6:14 is not directly concerned with the question of marriage itself. Further, Deuteronomy 7:3 was with respect to Jewish law.
The New Testament does not otherwise broach the topic. Over time, this has effectively left the matter to be specified by the various denominations themselves or be based on local customs or attitudes of the day. Of the Christian denominations, the Roman Catholic Church has the best-defined set of criteria on interfaith marriage recognition. The Eastern Orthodox have rules which are in most respects similar to the Catholics.
The Roman Catholic Church requires a dispensation for mixed marriages. The ordinary of the Catholic party has the authority to grant them. The baptized non-Catholic partner does not have to convert. Previously, the baptized non-Catholic partner had to agree to raise the children Catholic, but under current rules only the Catholic spouse must promise to do all that is in his or her power to do so. The non-Catholic partner must be made 'truly aware' of the meaning of the Catholic party's promise. Both parties must be instructed about the 'purposes and essential properties' of marriage, none of which can be excluded by either of the parties (thus neither party, including the non-Catholic, may exclude the permanence, exclusivity or openness to having children in the marriage, which is a standard condition of the validity of all marriages in Catholicism). It is forbidden to have a second religious ceremony in a different religion or one ceremony performed together by ministers of different religions. However, it is possible to waive the requirement of form (by granting a dispensation), so that for example one ceremony performed by the minister of another religion or a civil magistrate will be sufficient. Marriages with members Eastern rites are valid but illicit without proper observance of the form or dispensation from it, as long as a sacred minister is present and other canonical requirements are observed. 
The Roman Catholic Church has often discouraged marriages with Muslims and Jews, due to the fact that it is sometimes difficult to raise children in the faith after a marriage, especially if the woman is Catholic.
Marriages between a Catholic and an unbaptized person are not sacramental and fall under the impediment of disparity of worship (Code of Canon Law, Cn.1086 § 1).  They are invalid without a dispensation, for which authority lies with the ordinary of the place of marriage (Cn. 1086 § 2). In addition, the Catholic Church recognizes the Pauline privilege, wherein a Catholic may marry an unbaptized previously married person who consents to convert, but only if the unbaptized person's spouse refuses to become a Catholic also (similar to Muslim views on marrying previously-married non-Muslims).
- Max D. Younce, Is there any Scriptural advice concerning Protestants marrying Catholics?
- Are inter-faith marriages prohibited by the Bible?
- "Avoid marrying Muslims advises Portuguese cardinal". 15 Jan 2009.