This is part four of the miniseries "How to have a Happy Marriage: A Catholic Sacramental Point of View." This talk explores the premise and conditions of the validity of a sacramental union. It goes over the teachings of the Church by quoting from the dogmas on marriage and passages from the Catechism of the Catholic Church. This talk serves as a foundation for the fifth and last talk in the series where we bring together happiness in marriage with the sacramentality of Christian marriages.