Encyclopedias, Almanacs, Transcripts, and Maps
- Ollé-Laprune, Léon
- Ollendorff, Franz
- Ollendorff, Friedrich
- Olmedo
- Olmert, Ehud
- Olmo, Jacob Daniel ben Abraham
- Olmos, Andrés de
- Olomouc
- Olschwanger, Isaac Wolf
- Olshan, Isaac
- Olshausen, Justus°
- Olsson, Erik (Olai)
- Olsvanger, Immanuel
- Olyka
- Olympias, St.
- Omaha, Archdiocese of
- Oman, The Catholic Church in
- Omar Ibn al-KhaṬṬĀb°
- Omar, Covenant of
- Omer (Ayin) Hillel