High Quality Content by WIKIPEDIA articles! In the Roman Catholic Church an annulment is the procedure, governed by the Church`s Canon Law and the Catechism, whereby an ecclesial tribunal determines the sacrament of marriage was invalidly entered into. An annulment determines the Catholic marriage to be void at its inception. A "Declaration of Nullity" is not a legal dissolution of an existing civil marriage, but rather a determination that the sacrament of marriage was not entered into validly.