W. A. Mozart (1756-1791) did not seem to have any special occasion in mind when he composed the Missa Longa, K 262 in 1776. The Mass itself calls for elaborate instrumental interludes throughout, but does not include solo arias, so the Missa Longa cannot be classified as a missa solemnis (solemn Mass). It seems that missa longa (long Mass), a name used by Leopold Mozart for this particular Mass composed by his son, is a “hybrid” format between the missa brevis (short Mass) and the missa solemnis. Whereas a missa brevis is often embellished with solo arias, it routinely uses “telescoping” (simultaneous singing by different voices) of liturgical text, to reduce the duration of the Mass enough to meet certain time restrictions set by the “liturgists”. In the case of the missa longa in general, and the Mozart Missa Longa in particular, there is a tradeoff to keep the Mass of a shorter duration, yet liturgically correct - no telescoping of text in return for no extended composing for solo parts. The missa longa then is the middle ground in the tug-o-war between the liturgists and the musicians over how best to render Divine praise – through the use of heavenly words or of heavenly music.

The Mozart Missa Longa is scored for soprano, alto, tenor, and base (SATB) soloists, SATB choir, violin I and II, 2 oboes, 2 horns, 2 clarini (high trumpets), 3 trombones colla parte, timpani and basso continuo. The elaborate fugues at the end of the Gloria and Credo are masterful compositions that present special challenges for the Chorale. Look for the alternating soloists in the Dona nobis pacem at the end of the Agnus Dei. Mozart continued to compose sacred music during this period of his life, but he found himself transitioning towards composing more secular instrumental music as well as opera. In the summer of 1777, Mozart asked to be released from his employment with the Prince-Archbishop of Salzburg, Hieronymus Joseph Franz de Paula Graf Colloredo von Wallsee und Melz (r. 1771-1803). Prince-Archbishop Colloredo responded by dismissing both Mozart and his father.