Catechism of the Catholic Church §1191 — excerpt
Song and music are closely connected with the liturgical action. the criteria for their proper use are the beauty expressive of prayer, the unanimous participation of the assembly, and the sacred character of the celebration.
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.