Heinrich Isaac (c 1450-1517) was one of the most universal and versatile of all early composers and an important representative of the Netherlands school. He led a colourful life, reflected in his compositions in all musical forms and styles of the time in many languages, in a way that is comparable only with Orlande de Lassus almost 100 years later.

The main work on this recording is Isaac’s 6-part 'Missa paschalis'. It comprises the Ordinarium, the 'ordinary' sections: Kyrie, Gloria, Credo, Sanctus and Agnus Dei which are always present in the Mass. The Credo is, however, not present in the 'Missa paschalis'. In its place, this recording presents a 4-part composition by Isaac which is contained in Choir-book no.33 in the Thuringian State and University Library in Jena.

Like all Isaac’s Masses using Gregorian models, the 'Missa paschalis' follows the alternatim principle, the alternation between plainsong and polyphony. It is an exceptionally fine example of Isaac’s Mass settings and its Kyrie was one of few Mass settings by him that found its way into the choir-books of the Sistine Chapel in Rome, which has a tradition of performing such works unaccompanied. This performance by Ensemble Officium continues that tradition.