- O'BRIEN, Eugene
- O'CONNOR, Mark
- O'REGAN, Tarik
- OBUKHOV, Nikolai
- OCKEGHEM, Johannes
- ODDE, Bjørn Kåre
- ODEGAARD, Martin
- OEHLER, Thomas
- OEHRING, Helmut
- OFFENBACH, Jacques
- OGREN, Jayce John
- OKANO, Teiichi
- OLOFSSON, Kent
- OLSEN, Morten
- OLSEN, Ole
- OLSSON, Otto
- OLTHUIS, Kees
- ONDŘÍČEK, František
- ONSLOW, George
- OPPENHEIM, Henri
- ORBÁN, György
- ORFF, Carl
- ORLANDINI, Giuseppe Maria
- ORMANDY, Eugene
- ORTHEL, Léon
- ORTIZ, Diego
- ORTIZ, Gabriela
- OSCHER, Efrain
- OSPALD, Klaus
- OTAÑO, Nemesio
- OTTERLOO, Willem van
- OVERØYE, Odd Johan