The Liber Usualis contains virtually the entire corpus of Gregorian chant both for celebrations of the Mass, and for the hours of the Divine Office (e.g. Matins, Vespers). The texts of the Propers and Commons vary throughout the year; the texts of the Ordinary remain (usually) unchanged. *The Supplement consists of four individual items each with its own page numbering. The Liber Usualis was registered under US law in the name of Desclee & Co., under EFO-16387 following publication 1 October 1951; however no renewal was made.