Parentless Concepts
- Austrian Academy of Sciences
- Austrian Exchange Service
- Austrian Research Foundation
- Austrian Research Promotion Agency
- National Fund of the Republic of Austria for Victims of National Socialism
- Old Testament in Arabic
- Omar & Ossman & Aly carmina
- Opala, Elias
- open access
- opera
- Opus Veteris Testamenti Arabicum, praecipue Prophaetae
- Orient
- original
- Orlandini, Nicolò
- Orta, Garcia de
- Osiander, Andreas
- Osman II
- Osóno, Jerónimo
- Ostermayer, Gerardus
- Ostermayr, Gerhard
- other
- Otto of Freising
- Otto, Julius Konrad
- Ottokar I