1 (D 18) in mixed keys was composed by Franz Schubert in 1810 or 1811.
A partial autograph of the composer kept in the Vienna City Library has the date 1812 written on the cover.
[2] As such it may be Schubert's earliest extant completed multi-movement work for more than one player.
The quartet was played in 1812 by the quartet of Schubert's family (his father Franz Theodor, his brothers Ignaz and Ferdinand, and Schubert himself playing viola).
D 18 is the only remaining of a set of three early string quartets "in changing, undefined" key signatures by Schubert.