Author
- Order of the Immaculate Conception1
- Orderic Vitalis1
- Orosius1
- Osbern of Gloucester1
- Oswald Corda1
- Ottavio Strada1
- Ottmar Luscinius1
- Otto di guardia e balia (Florence, Tuscany)1
- Palazzo degli Anziani1
- Papias1
- Parliament of Great Britain1
- Paschal II1
- Paschualis Bernardus1
- Patrick Graham, 1st Lord Graham1
- Paul IV1
- Paul the Deacon1
- Paul, of Cologne1
- Pedro Henrique de Bragança1
- Pedro Luis de Borja Lanzol de Romaní1
- Pedro de Serra1