路德維希‧范‧貝多芬（Ludwig van Beethoven, 1770-1827）其人其樂不只為音樂創作樹立典範，也為人生哲學提供省思，是西洋音樂史深具影響力的音樂家。貝多芬大多數作品皆為不朽之作，其中貝多芬終其一生創作不歇的《三十二首鋼琴奏鳴曲》，猶如貝多芬一生的傳記，不僅細載著貝多芬生命的歷程，亦呈現貝多芬音樂風格的演變。本研究旨在探討貝多芬《鋼琴奏鳴曲，作品九十》（Piano Sonata, Op. 90）之源流與發展。首先，探討貝多芬作品分期與風格；其次，探討貝多芬《鋼琴奏鳴曲，作品九十》之作品特質；最後，探討貝多芬《鋼琴奏鳴曲，作品九十》之傳承與影響。經本研究發現，《鋼琴奏鳴曲，作品九十》植基於古典奏鳴曲形式與貝多芬既有之創作手法，並輔以內蘊而外顯之情感表述，引領貝多芬晚期鋼琴奏鳴曲創作風格，是為貝多芬中期銜接至晚期創作之轉捩點。

Ludwig van Beethoven (1770-1827) is one of the most influential composers in the history of Western music. His works set models for music compositions, and his philosophy inspires us to consider about human life. Most of Beethoven’s works are admirable, such as piano sonatas were written throughout his life. Thirty-two Piano Sonatas can be interpreted as Beethoven's biography. They demonstrate the linear progress of his life as well as reveal the changes of compositional style. This study especially focuses on the origin and development of Beethoven Piano Sonata, Op. 90. In this article, firstly, the three-period divisions and styles of Beethoven’s works are mentioned; then, the author analyzes the musical characteristics of Piano Sonata, Op. 90. Finally, the author investigates the legacy and influence of this piano sonata. Beethoven Piano Sonata, Op. 90 origins from classical sonata form and his compositional techniques are refined with strong emotion, which becomes the main style of Beethoven’s late piano sonatas. Therefore, Beethoven Piano Sonata, Op. 90 can be seen as his turning point in the middle period to the late period.