Symphony No. 9 by Gustav Mahler was written between 1908 and 1909, and was the last symphony that he completed. It is actually his tenth symphonic work, as Mahler gave no ordinal number to his symphonic song-cycle Das Lied von der Erde. A typical performance takes about 75 to 90 minutes.
Though the work is often described as being in the key of D major, the tonal scheme of the symphony as a whole is progressive. While the opening movement is in D major, the finale is in Db major.