- Nofrio, Jacopo di1
- Norbert, of Xanten, Saint, approximately 1080-11341
- Novitiate1
- Oaths1
- Occasional verse1
- Occultism1
- Octavia, Empress, consort of Nero, Emperor of Rome, approximately 42-621
- Odes1
- Odes, Latin (Medieval and modern)1
- Oedipus (Greek mythological figure)1
- Official Papers: National and Local Affairs1
- Ordinatio (Duns Scotus, John)1
- Oria, Johannes d'1
- Origen1
- Orlandini, Stefano1
- Orthodox Eastern Church1
- Orto, Giovanni dall'1
- Paffiere, Arcangelo1
- Paffiere, Matteo1
- Pagani, Angiola1