Komponisten von A-Z
- Oakley, George (1979–)
- Obadike, Mendi & Keith (1973–)
- Obermüller, Karola (1977–)
- Obrecht, Jakob (1457–1505)
- O'Brien, Charles (1882–1968)
- O'Carolan, Turlough (1670–1738)
- Ockeghem, Johannes (1430–1497)
- O'Connor, Mark (1962–)
- Odegaard, Henrik (1955–)
- Odeh-Tamimi, Samir (1970–)
- Oehring, Helmut (1961–)
- Oestreich, Carl (1800–1840)
- Ofenbauer, Christian (1961–)
- Offele, Winfried (1939–)
- Offenbach, Jacques (1819–1880)
- Ohana, Maurice (1914–1992)
- Ohguri, Hiroshi (1918–1982)
- Ohki, Masao (1901–1971)
- Ohrn, Konrad (1950–)
- Ohse, Reinhard (1930–)
- Ohzawa, Hisato (1907–1953)
- Olavide, Gonzalo de (1934–2005)
- Olbrisch, Franz Martin (1952–)
- Oldham, Kevin (1960–1993)
- Oliveros, Pauline (1932–2016)
- Olofsson, Kent (1962–)
- Olsen, Ole (1850–1927)
- Olsen, Morten (1961–)
- Olsson, Otto (1879–1964)
- Ona, Erik (1961–)
- Onslow, Georges (1784–1852)
- Ore, Cecilie (1954–)
- Orefice, Giacomo (1865–1922)
- O'Regan, Tarik (1978–)
- Orejon y Aparicio, Jose de (1705–1765)
- Orff, Carl (1895–1982)
- Orlandini, Giuseppe Maria (1676–1760)
- Ornstein, Leo (1892–2002)
- Orologio, Alessandro (1555–1633)
- Orr, Robin (1909–2006)
- Orr, Buxton (1924–1997)
- Orr, Charles Wilfred (1893–1976)
- Orthel, Leon (1905–1985)
- Ortiz, Pablo (1956–)
- Ortiz, Diego (1510–1558)
- Osborne, Charles (1927–)
- Osborne, George Alexander (1806–1893)
- Oscher, Efrain (1974–)
- Ospald, Klaus (1956–)
- Ostendorf, Jens-Peter (1944–2006)
- Ostrcil, Otakar (1879–1935)
- Oswald, Henrique (1852–1931)
- Oswald, Andreas (1634–1665)
- Otano, Nemesio (1880–1956)
- Ott, Daniel (1960–)
- Otte, Hans (1926–2007)
- Ourkouzonov, Atanas (1970–)
- Ozdemir, Burak (1984–)
- Ozi, Etienne (1754–1813)
- Ozzard-Low, Patrick (1958–)
- van Otterloo, Willem (1907–1978)
- von Ordonez, Karl (1734–1786)
- von Wolkenstein, Oswald (1377–1445)