The Grand Duo Concertant, Opus 48, J204, is a three-movement work for clarinet and piano composed by Carl Maria von Weber from 1815 to 1816. It is a virtuosic piece for both instruments. Weber most likely composed the work for himself (on piano) and his friend Heinrich Baermann, a leading clarinettist of the era, although it has also been suggested that the intended clarinettist was Johann Simon Hermstedt.
The three movements are as follows:
- Allegro con fuoco
- Andante con moto
- Rondo: allegro
The second and third movements were completed before the first and were probably performed in 1815 for King Maximilian I Joseph of Bavaria at the Nymphenburg Palace. During its composition, Weber designated the work as a sonata, but abandoned that title upon its completion. This decision reflected the work's character as more of a showcase for two virtuosos than a conventionally structured and integrated work. The first movement is in sonata form, the second movement is an Andante in C minor, and the finale is a lilting rondo in E-flat major. The British music critic John Warrack suggests the work could be referred to as a "double concerto without orchestra", reflecting the highly virtuosic roles for both performers.