In music, Op. 12 stands for Opus number 12. Compositions that are assigned this number include:

• Adès – Arcadiana
• Barber – Essay for Orchestra
• Beethoven – Violin Sonata No. 1
• Beethoven – Violin Sonata No. 2
• Beethoven – Violin Sonata No. 3
• Braunfels – Prinzessin Brambilla
• Dvořák – String Quartet No. 6
• Elgar – Salut d'Amour
• Korngold – Die tote Stadt
• Luigini – Ballet égyptien
• Mendelssohn – String Quartet No. 1
• Mendelssohn – String Quartets
• Nielsen – Hymnus amoris
• Pierné – Piano Concerto
• Rachmaninoff – Caprice bohémien
• Saint-Saëns – Oratorio de Noël
• Schumann – Fantasiestücke, Op. 12
• Sibelius – Piano Sonata in F major
• Vivaldi – Six Violin Concertos, Op. 12
• Ysaÿe – Poème élégiaque in D minor, Op.12