Dukes | Titles by Rank
- Dukes of Oppeln
- Dukes of Orbino
- Dukes of Orkney
- Dukes of Orleans
- Dukes of Ormonde
- Dukes of Orta
- Dukes of Ossada
- Dukes of Östergötland
- Dukes of Osuna
- Dukes of Otrante
- Dukes of Otrante
- Dukes of Pádua
- Dukes of Paliano
- Dukes of Palma
- Dukes of Palma de Maiorca
- Dukes of Palmela
- Dukes of Palombara
- Dukes of Parcent
- Dukes of Parma
- Dukes of Parque
- Dukes of Pastrana
- Dukes of Peñafiel
- Dukes of Peñaranda de Bracamonte
- Dukes of Peñaranda de Duero
- Dukes of Penthièvre
- Dukes of Picquigny
- Dukes of Pietratagliata
- Dukes of Piney
- Dukes of Piney-Luxembourg
- Dukes of Pinohermoso
- Dukes of Pistoia
- Dukes of Plaisance
- Dukes of Plasencia
- Dukes of Poggio Nativo
- Dukes of Poix
- Dukes of Poli
- Dukes of Polignac
- Dukes of Polo
- Dukes of Polónia
- Dukes of Pomar
- Dukes of Pomerania
- Dukes of Pomerânia-Barth
- Dukes of Pomerânia-Rügen
- Dukes of Pomerânia-Stargard
- Dukes of Pomerânia-Stettin
- Dukes of Pomerânia-Stolp
- Dukes of Pomerânia-Wolgast
- Dukes of Popoli
- Dukes of Portella
- Dukes of Portland