Encyclopedias, Almanacs, Transcripts, and Maps
- Orbis Books
- Orchard Lake Schools
- Ordeal of Jealousy
- Order of Christ
- Order of the Swan
- Ordinals, Roman
- Ordinaries, Ecclesiastical
- Ordinations in the Roman Rite
- Ordines Judiciarii
- Ordman, Jeannette
- Ordo, Roman
- Ordzhonikidze
- Oré, Luis Gerónimo de
- Oreb and Zeeb
- Oregon School Case
- Oregon, Catholic Church in
- Orel
- Oremus
- Oren, Ram
- Oren, Yiẓḥak