Encyclopedias, Almanacs, Transcripts, and Maps
- Otto I (The Great), Emperor
- Otto II, Emperor
- Otto III, Emperor
- Otto of Bamberg, St.
- Otto of Cappenberg, Bl.
- Otto, Rudolf
- Otto, Rudolph°
- Ottobeuren, Abbey of
- Ottolenghi
- Ottolenghi, Giuseppe
- Ottolenghi, Joseph ben Nathan
- Ottolenghi, Moses Jacob
- Ottolengo, Samuel David ben Jehiel
- Ottoman Turks
- Ottonian Renaissance
- Otwock
- Ouaknin, Marc-Alain
- Oudtshoorn
- Ouen of Rouen, St.
- Oulif, Charles Narcisse