Encyclopedias, Almanacs, Transcripts, and Maps
- Ochs, Siegfried
- Ockhamism
- Octobrists
- Octoechos
- Oddi, Diego, Bl.
- Odenathus and Zenobia
- Oderisius, Bl.
- Odessa Committee
- Odilia, St.
- Odilo of Cluny, St.
- Odin, John Mary
- Odo (Eudes) of Châteauroux°
- Odo (Eudes) of Sully°
- Odo (Oda) of Canterbury, St.
- Odo of Cambrai, Bl.
- Odo of Cambrai°
- Odo of Châteauroux
- Odo of Cluny, St.
- Odo Rigaldus
- Odoric of Pordenone, Bl.