"Sonata quasi una fantasia" is a piano sonata composed by Ludwig van Beethoven in 1801. It is often considered a bridge between the classical sonata form and the more free-form structures of the Romantic era. The piece is notable for its lyrical themes and innovative use of contrasting sections, which give it a unique character. The sonata consists of four movements, each showcasing Beethoven's mastery of melody and harmony. The first movement, marked "Allegro," introduces a bold theme, while the subsequent movements explore various moods and tempos. This work reflects Beethoven's evolving style and his departure from traditional forms, making it a significant contribution to piano literature.