||One of the extraordinary innovations found in Mahler's symphonies is the use of progressive tonality as a vehicle to express emotional transformation. Two of Mahler's four "Wunderhorn" symphonies, the Second and Fourth, both progress away from the original tonic and end in a mediant or submediant key to express, respectively, the miracle of resurrection and a child's vision of Heaven. This tonal shift by a third, though original, is considered still conventional by late-Romantic standards. The Fifth Symphony, however, decidedly departs from tradition as it boldly journeys from C# minor to D major to symbolize the triumph of joy over tragedy. The questions of why and how the tonal shift and mode change are connected to the material of the work are addressed in the present study that analyses the symphony's most significant melodic and harmonic processes and focuses on the influence of a single pitch, A, in the unfolding of the music. In its comprehensive scope, the study systematically traces these processes as they develop through the entire work and examines questions not previously addressed in writings by major authors. How pitch A participates in conveying the transformation of tragedy into joy is discussed under the following topics: the melodic stabilization of pitch A; pitch A as a pivot in the assertion of D major; the submediant relationship; whole-tone elements; and a Schenkerian perspective of each movement and the entire symphony.