Liber Usualis

The Liber Usualis is a book of commonly used Gregorian chants in the Catholic tradition, compiled by the monks of the Abbey of Solesmes in France.

This 1,900-page book contains most versions of the ordinary chants for the Mass (Kyrie, Gloria, Credo, Sanctus, and Agnus Dei), as well as the common chants for the Divine Office (daily prayers of the Church) and for every commonly celebrated feast of the Church Year (including more than two hundred pages for Holy Week alone). The "usual book" or "common book" also contains chants for specific rituals, such as baptisms, weddings, funerals, ordinations, and benediction. This modal, monophonic Latin music has been sung in the Catholic Church since at least the sixth century and through the present day.

An extensive introduction explains how to read and interpret the medieval musical notation (square notation of neums or neumes). A complete index makes it easy to find specific pieces.

The Liber was first edited in 1896 by Solesmes abbot Dom André Mocquereau (1849–1930). After the Second Vatican Ecumenical Council (opened by Pope John XXIII in 1962) allowed in the constitution on the liturgy Sacrosanctum Concilium the vernacular (local language) to be used in Church rites, its use has decreased, although the same council mandated that Gregorian Chant should retain "pride of place" in the liturgy (Sacrosanctum Concilium, 116.). Gregorian chants are still sung in most monasteries and some churches and in performances by groups dedicated to its preservation.