Those getting married in the Catholic Church must be baptized Christians, not too closely related, in good standing with the church, of the opposite sex and free to marry. The term "free to marry" is often the biggest obstacle in prospective Catholic marriages. If someone has been married previously, his spouse must either be deceased, or he must receive a nullification from the Church. A legal divorce is not enough.
A person does not have to be Catholic to marry a Catholic partner in the church. However, he must be a baptized Christian, and the Catholic partner must receive permission from the presiding bishop to marry the non-Catholic. The Catholic church does not allow marriages between first cousins and did not allow marriages between second cousins until 1983.
The Catholic church only recognizes marriages between one man and one woman. It does not recognize any type of union or relationship between two men or two women. The couple also needs to be in good standing with the church. This may mean, for example, if the couple have been living together, they must spend sufficient time living separately before marrying. A Catholic politician who supports policies against Church laws may also be considered not to be in good standing with the church.