Encyclopedias, Almanacs, Transcripts, and Maps
- Octobrists
- Odell, Jonathan
- Odell, William
- Odetta (Gordon, Odetta Holmes Felious)
- Odoyevsky, Vladimir Fyodorovich
- Offenbach, Jacques
- Office of Emergency Management
- Officeholding
- Official Nationality
- Ogarkov, Nikolai Vasilevich
- Ogbu, John
- Ogden, Aaron
- Ogden, Matthias
- Oghkwaga
- Ohio Company of Associates
- Ohio Company of Virginia
- Oklahoma City Federal Building Bombing
- Okolnichy
- Okomfo Anokye
- Okudzhava, Bulat Shalovich