Metamorphosen, study for 23 solo strings (TrV 290, AV 142) is a composition by Richard Strauss, scored for ten violins, five violas, five cellos, and three double basses, of approximately 26 minutes in duration. It was composed during the closing months of the Second World War, from August 1944 to March 1945. The piece was commissioned by Paul Sacher, the founder and director of the Basler Kammerorchester and Collegium Musicum Zürich, to whom Strauss dedicated it. It was first performed in January 1946 by Sacher and the Collegium Musicum Zürich, with Strauss conducting the final rehearsal . In 1996, Rudolf Leopold wrote a version for Septet .