Vesperae solennes de confessore (Solemn Vespers for a Confessor), K. 339, is a sacred choral composition written by Wolfgang Amadeus Mozart in 1780. It is scored for SATB choir and soloists, violin I, violin II, 2 trumpets, 3 trombones colla parte, 2 timpani, and basso continuo (violoncello, double bass, and organ, with optional bassoon obbligato).
The composition was written for liturgical use in the Salzburg Cathedral. The title "de confessore" was not Mozart's own, having been added to his manuscript later. It suggests the work was intended for vespers held on a specific day on the liturgical calendar of saints ("confessors"); however, the saint in question has not been conclusively established, and may not have existed. This was Mozart's final choral work composed for the cathedral.
Structurally, it is very similar to K. 321 Vesperae solennes de Dominica, composed in 1779. The composition is divided into 6 movements; as in Dominica, a setting of the Minor Doxology (Gloria Patri) concludes all movements, each recapitulating the opening themes. The first three psalms are scored in a bold, exuberant manner, contrasting with the strict, stile antico counterpoint of the a cappella fourth psalm, and the tranquility of the fifth movement. The Magnificat sees a return to the style of the opening settings.