- Ochoa family1
- Odyssey (Homer)1
- Orden de Alcántara1
- Orden de Santiago1
- Order of the Golden Fleece1
- Orders of knighthood and chivalry2
- Ordinances, Municipal1
- Oria, Johannes d'1
- Ortiz family1
- Ottava rimas, Spanish2
- Ovando, Nicolás de, approximately 1460-15111
- Oviedo family1
- Oviedo, Francisco de, 1728-1
- Oviedo, Gregorio de, 1721-17961
- Oviedo, Nicolás de, 1725-1
- Pablo de Santa Maria, Bishop of Burgos, approximately 1351-14351
- Painted books1
- Painted leather bindings4
- Palomino family1
- Paper1