This article relies largely or entirely on a single source. (May 2019)
Disparity of cult, sometimes called disparity of worship (Disparitas Cultus), is a diriment impediment in Roman Catholic canon law: a reason why a marriage can not be validly contracted without a dispensation, stemming from one person being certainly baptized, and the other certainly not baptized.
The reasons for this impediment is that the marriage will not be a sacrament with one spouse unbaptized, that the unbaptized person's views on marriage may be incompatible with the Catholic views, and that such a marriage may hinder the practice of religion on part of the Catholic spouse and any children.
Disparity of worship does not affect the marriage of a Catholic or baptized non-Catholic with one whose baptism, even after careful investigation concerning the baptismal ceremony or its validity, remains doubtful. Neither does it in any way influence the marriage of two who, after diligent examination, are still considered doubtfully baptized.
A marriage between a Catholic and a baptized non-Catholic is a mixed marriage. Though sometimes referred to by this term, the permission of the bishop is required merely to make the union licit; the marriage is valid but illicit without it.
Disparity of worship can be dispensed for grave reasons, and on the promises (usually written) from the spouses: the unbaptized not to interfere with the spouse's practice of religion or the raising of the children in religion, the Catholic to practice the Catholic religion and raise the children in it.