Catechism of the Catholic Church §1662 — excerpt
Marriage is based on the consent of the contracting parties, that is, on their will to give themselves, each to the other, mutually and definitively, in order to live a covenant of faithful and fruitful love.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.