The Missa brevis contains a set of Gregorian chants (Kyrie, Gloria, Credo, Sanctus, Agnus Dei). This selection provides chants simple to learn and to sing. The selected Sanctus and Agnus Dei are the best known, since they appear also in the Masses of the Dead.
For new communities interested to be initiated to Gregorian chant, it provides a beautiful and shorter alternative for the Missa de Angelis, which tends to be overused by newbies. It uses the Kyrie 16, Gloria 15, Credo 1, Sanctus 18 and Agnus Dei 18 from the Graduale Romanum.
The scores below come from Gregobase, a database of Gregorian scores.
Agnus Dei XVIII