- Orthodox Eastern Church1
- Ospedale degli Innocenti (Florence, Italy)1
- Otto I, Holy Roman Emperor, 912-9731
- Ovando, Nicolás de, approximately 1460-15111
- Oviedo family1
- Oviedo, Francisco de, 1728-1
- Oviedo, Gregorio de, 1721-17961
- Oviedo, Nicolás de, 1725-1
- Paganelli, Roberto1
- Pakhomiĭ Logofet, monk, active 15th century1
- Panama--Panama1
- Paolo, Stefano di1
- Papal nuncios1
- Paper1
- Papi, Giovanni1
- Papi, Pasquino1
- Parent and child (Law)1
- Paul IV, Pope, 1476-15591
- Paul V, Pope, 1552-16211
- Peasants' War (1524-1525)1