The two Masses K.139 and K.66 predate Mozart's permanent appointment in Salzburg and were written for particularly festive occasions. The Wainsenhausmesse K.139 dates from 1769 and was composed for the dedication of the new Orphanage church in Vienna's Rennweg, while the Dominicus Mass K.66 was written in 1769 fir the first Mass to be celebrated by Dominicus Hagenaur, a friend of Mozart's youth. Both works are more relaxed in tone than those associated with the Salzburg Cathedral tradition and are also more opulently scored, with oboes, horns, trumpet and timpani.

Precise guidelines existed for church music in the Salzburg and, more especially, for the Masses that were held in the town. These were not allowed to be unduly secular in style, in other words, neither operatically virtuosic nor too lavishly orchestrated. Nor could they exceed a certain length, as Mozart makes clear in a letter of 1776 to his teacher of counterpoint, Padre Martini, in Bolonga: "My father is in the service of the Cathedral and this gives me an opportunity of writing as much church music as i like. [...] Our church music is very different from that of Italy, since a mass [...] must not last longer than three quarters of an hour. This applies even to the most Solemn Mass said by the Archbishop himself".

When Mozart wrote these lines in 1776, he had already been Konzertmeister in the Salzburg court orchestra for four years. Four masses date from 1776, all in C major, including the composer's eleventh contribution to the genre, the Credo Mass K.257, which owes its name to a particularly telling compositional device: the lengthy text of the Credo is interrupted no fewer than sixteen times by motto-like calls of "Credo" by full chorus and individual voices. These are clear signs not only here but also in the last of Mozart's Salzburg Masses, K.337, of the brevity and concentration enjoined upon the composer: musical ideas can only be hinted at, never spun into their proper length.

In 1776 Mozart also wrote the Litaniae de venerabili altaris sacramento K.243, the last and longest of his four Litanies. With its remarkable dimensions and unmistakable borrowings from Italian opera, this solemn work was evidently one that Mozart prized highly, since as late as 1790 he listed it in a job application to Archduke Franz of Austria, citing it as evidence of his 'familiarity' with the style of church music.

After five years serving the Salzburg court, Mozart handed in his notice and turned his back on the town in September 1777. Traveling via Munich, Augsburg and Mannheim, he arrived in Paris in March 1778, but failed to forge the hoped-for-contacts or find a permanent appointment. His mother died in Paris and his love of Aloysia Weber, the sister of his future wife Constanze, remained unrequited. Having suffered these disappointments, Mozart was left with no alternative but to return to Salzburg, and from 1779 to 1781 he was again employed in the Archbishops service. Although this return to the monotony of the church service and to the provincialism of a town that lacked an opera house and theater (Mozart, as we well know, was fascinated by the stage) must have pained him deeply, it did not prevent him from writing a series of important sacred works: these include Regina coeli K.276 (a work cast in the form of a single arching curve, each of its two verses ending with a quotation from Handel's Messiah), the Vespers K.339, the Messa solemnis K.337 (Mozart's last Salzburg Mass) and, above all, the Coronation Mass in C major K.317. This lavishly scored work was completed by Easter 1779, only two months after the composers return to Salzburg, but it was not until twelve years later that it received its familiar title, when it was performed under Antonio Selieri at the coronation of Leopold II in Prague. The magnificent choral movements that open the Kyrie, Gloria and Credo no doubt encouraged Salieri to revive the piece for such a festive occasion.

Mozart broke with Salzburg in 1781 and moved to Vienna. As a free-lance artist he was no longer under any obligation to compose church music, but this did not stop him embarking in 1783 on a Mass in C minor, K.427, evidently in fulfillment of a self-imposed vow following his marriage with Constanze. In the even, the work remained unfinished, although a version of it was performed in St Peter's, Salzburg, in 1783 with Constanze Mozart as one of the two soprano soloists. It is a highly heterogeneous piece in which powerful polyphonic choruses of an almost archaic and statuesque character (listen, for instance, to the elaborate fugal "Hosanna" for double choir) are contrasted with operatic solo numbers such as the "Laudamus te", with its florid writing for soprano solo.