Metamorphosen, study for 23 solo strings (TrV 290, AV 142) is a composition by Richard Strauss for ten violins, five violas, five cellos, and three double basses, typically lasting 25 to 30 minutes. 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 on 25 January 1946 by Sacher and the Collegium Musicum Zürich, with Strauss conducting the final rehearsal.