Catholics regard marriage as one of the seven sacraments received during their lifetime. The seven sacraments are baptism, confirmation, Holy Eucharist, penance, holy orders, matrimony and the last rites. The church instills that a marriage should be between a baptized man and woman. In the Old Testament, marriage between these two individuals was seen as a symbol much like that of the relationship between the people and God. To be more precise, in the letter to the Ephesians, it states that this is a symbol between the church and Christ.
Although, the Catholic Church would prefer that a Catholic marry a Catholic, it is not forbidden to marry outside the church to non-Christians. Those marriages, however, are considered non-sacramental and may still be valid in the eyes of Catholic Church. The Catholic Church, like other institutions and states, have certain requirements and Catholics are encouraged to follow them. The Catholic Church requires that a valid marriage contain four elements: 1) a person is free to marry, 2) these persons can freely consent to this marriage, 3) that these person’s intent is to marry for life, be faithful, and be open to the possibility of having children, and 4) the consent of this marriage should be in the presence of an authorized church minister and two witnesses should be present during this union. (The last condition should be approved by a church authority). If a person is marrying a non Catholic, they must seek person from the local bishop to do so.
Catholics believe that a wedding should be held in a church as this is not just a social affair, but rather a church event. If, however, an individual wishes to marry outside the church setting, they must obtain approval from a local bishop.
If a Catholic is marrying a non Catholic, the children do not necessarily have to be brought up in this faith; however, the Catholic spouse must promise that they will do everything in their power to raise the children in this preferred religious setting.
If the case ever arises for an annulment of marriage through the Catholic Church, it is done with the premise that one of the essential four elements stated above fell short. This is different from the usual civil divorce in that it does not erase things that were in place, but only it is a declaration that there was never a valid marriage from the onset. In the case of nullity, it does not impact the children’s legitimacy whatsoever because the church recognizes that the couple was married when the children were conceived.
On the overall view of a sacramental marriage there are some differences between Catholics and Protestants. A Protestant believes in only two sacraments; whereas, Catholics believe in seven. A Protestant believes in the “The Lord’s Supper” and in baptism. Catholics regard that it is inconceivable for baptized people to marry validly without their union being a sacrament, so there are some differences of opinion on this very issue. Catholics believe this due to the Canon of the Second Vatican Council the Constitution on the Church in the Modern World. Here, it asserts that Christ declared that between the baptized raises the marriage covenant to the dignity of a sacrament. The following paragraph is even more precise: a valid marriage cannot exist between two baptized persons without it being by that very fact a sacrament.
As you can see, there are some clear definitions on the laws of marriage through the Catholic Church. If a Catholic person is not sure as to whether their marriage is considered a sacramental or non-sacramental marriage, the best place to begin asking questions is to your local priest.