The Roman Gradual (Graduale Romanum) and the Liber Usualis are the most ignored and almost universally rejected official liturgical books of the Roman Catholic Ritual, being the fundamental Catholic liturgical music books. Is it any wonder our parish Masses are so pedestrian and the music is so bad and no one knows any of the Mass is Latin? The neglect of this treasure of Church patrimony is part of the bias against the official Latin language of the Church and is contrary to the liturgical norms and the canonical norms regarding seminary formation: e.g. "The Church recognizes Gregorian chant as being specially suited to the Roman liturgy. Therefore, other things being equal, it should be given pride of place in liturgical services." Sacrosanctum Concilium, 116.
How can the most prized become the most despised!...almost overnight! The Holy Father expressed the impossibility of such a radical rejection of our Latin liturgical heritage in his Summorum Pontificum Letter to the Bishops: "In the history of the liturgy there is growth and progress, but no rupture. What earlier generations held as sacred, remains sacred and great for us too, and it cannot be all of a sudden entirely forbidden or even considered harmful. It behooves all of us to preserve the riches which have developed in the Church’s faith and prayer, and to give them their proper place."
Both books are completely accessible on the internet gratis at musicasacra.com.