| Ono, Tadasuke (? - ) Japan |
| Oomen, Paul (1982 - ) The Netherlands |
| Oorebeek, Christina Viola (1944 - ) The Netherlands |
| Oosten, Roel van (1958 - ) The Netherlands |
| Oosterveld, Ernst (1951 - ) The Netherlands |
| Oostrom, Tom van (? - ) U.S.A. |
| Opalka, Tomasz Jakub (1983 - ) Poland |
| Opazo Muñoz, Mauricio (1969 - ) Spain |
| Opitz, Bernhard (1967 - ) Germany |
| Opitz, Erich (1912 - 2001) Austria |
| Oppedisano, Marco (1971 - ) U.S.A. |
| Oppo, Franco (1935 - ) Italy |
| Orbán, György (1947 - ) Hungary |
| Orbón, Julián (1925 - 1991) Cuba |
| Ordway, Scott J. (1984 - ) U.S.A. |
| Ore, Østen Mikal (1967 - ) Denmark |
| Orekhov, Sergei (1935 - 1998) Russia |
| Orenstein, Joyce E. (1939 - ) U.S.A. |
| Orff, Carl (1895 - 1982) Germany |
| Orgad, Ben-Zion (1926 - 2006) Israel |
| Orkin, Yevgeni (1977 - ) Ukraine |
| Orosco, Maurício (? - ) Brazil |
| Orozco, Keyla (1969 - ) Cuba |
| Orr, Buxton (1924 - 1997) United Kingdom |
| Orrego-Salas, Juan (1919 - ) Chile |
| Orsi, Andrea (1955 - ) Italy |
| Orsolino, Federico (1918 - 1993) Italy |
| Ortega, Jesús (1935 - ) Cuba |
| Ortega, Miguel (1963 - ) Spain |
| Ortega Blanco, José (? - 1977) Spain |
