String Quartets Op. 18 No. 5 and Op. 59 No. 1 are chamber works by Ludwig van Beethoven, composed and published in 1800–1801 and 1806–1808 respectively. The earlier quartet reflects Beethoven's early Classical idiom with balanced forms, clear textures and lyrical writing, while Op. 59 No. 1 demonstrates his middle-period expansion of the quartet genre through larger-scale structures, increased harmonic daring, intensified rhythmic drive and greater technical demands, signalling a move towards more ambitious and exploratory chamber music in his career.