The Missa brevis in D minor, K. 65/61a, is a mass composed by Wolfgang Amadeus Mozart (12 years old at the time) and completed on 14 January 1769. It is scored for SATB soloists and choir, violin I and II, 3 trombones colla parte, and basso continuo.
The long held belief, based on Sigismund Keller's assertion in 1873, that this mass was first performed on 5 February 1769, the pre-Lenten Sunday of Quinquagesima, in the University of Salzburg's Kollegienkirche to open a forty-hour vigil, has later been shown as untenable. As a Lenten mass, the Gloria could not have been performed.
This is Mozart's shortest setting of the Order of Mass, and his only missa brevis set in a minor key.
The mass is divided into six movements.