"In the Classical period, and well into the 19th century, piano trios were something of a musical fashion accessory. There was thus good reason for Beethoven also to engage with the genre, following the example set by Haydn and Mozart. He left 13 piano trios in all.
The works contained in Volume III almost all present a few peculiarities: opus 44 is also not a complete trio, for instance, but consists of only one single variation movement! WoO 37, written while Beethoven was still in Bonn, is striking for its scoring (piano, flute and bassoon). He wrote WoO39 for Maximiliane, youngest daughter of the Brentano family, ''to encourage her piano playing''. Op. 38 is an arrangement of the Septet op. 20 for piano, clarinet and violoncello, and the last piece has come down to us only in one sketchbook from Beethoven's Bonn period. None of these works has the weight of Beethoven's major piano trios nevertheless, they remain witnesses to his supeme artistry. "