This study analyzes the most prominent manifestations of harmonic expansion and tension in Bill Evans’ harmonic techniques, focusing on appoggiatura and polychords. These two techniques represent Evans’ characteristic harmonic progressions that dramatically induce and resolve tension. While Evans employs numerous other idiosyncratic harmonic techniques, these two serve as cornerstones of all Jazz harmonic development, rooted in his assimilation of classical music into Jazz piano. Appoggiatura elucidates Evans’ method of inducing harmonic tension and resolution through the polyphonic use of non-harmonic tones. Polychord is dissected into two categories: one comprising diatonic scales and the other involving altered scales. The study explores how Evans employed diverse Polychords based on harmonic tension and the flow of the musical piece. Through the analysis of Bill Evans’ solo piano composition “We Will Meet Again”, this research examines how harmonic expansion unfolds in compositional music and elucidates how Evans employed these techniques in his performances to actualize and crystallize his unique harmonies.