Encyclopedias, Almanacs, Transcripts, and Maps
- 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
- Oultremont, Emilie d’, Bl.
- Our Lady Mother of Mercy, Brothers of
- Our Lady of Charity, North American Union Sisters of
- Our Lady of Good Counsel
- Our Lady of Perpetual Help (Succour)
- Our Lady of the Garden, Sisters of