Piano Sonata no. 14 in A minor, D.784, op. posth.143

Franz Schubert's Piano Sonata in A minor, D 784 (posthumously published as Op. 143), is one of Schubert's major compositions for the piano. Schubert composed the piano sonata in February 1823, perhaps as a response to his illness the year before. It was however not published until 1839, eleven years after his death. It was given the opus number 143 and a dedication to Felix Mendelssohn by its publishers.

The D 784 sonata, Schubert's last to be in three movements, is seen by many to herald a new era in Schubert's output for the piano, and to be a profound and sometimes almost obsessively tragic work.