- Nuti, Giovanni, 1952-1
- Octavia, Empress, consort of Nero, Emperor of Rome, approximately 42-621
- Odilo, Saint, Abbot of Cluny, 962-1048 or 10491
- Odo, Saint, Abbot of Cluny, approximately 879-9421
- Oedipus (Greek mythological figure)1
- On the generation of animals (Aristotle)1
- Orden de Alcántara1
- Origen1
- Oviedo, Rodrigo de, active 1514--Trials, litigation, etc1
- Pago, Sapia di1
- Paleography1
- Palimpsests1
- Palmistry1
- Panel-stamped bindings1
- Papal briefs1
- Papal legates1
- Parables1
- Parchment (Paper)1
- Parishes1
- Passion plays1