Prince or Princess is a title used in Westeros, Essos and the Summer Islands.
The Rhoynar civilization was formed by independent city-states, each of which was ruled by a Prince or Princess.
Among the Free Cities, the Prince of Pentos, as well as the three Princes of Lorath, are the figurehead rulers of their respective cities. True power lies in the Magisters.
In Westeros, the title is usually conferred to the children of the king. Prior to the War of the Usurper, the heir to the king on the Iron Throne held the title "Prince of Dragonstone",  and one his other sons held the title "Prince of Summerhall". The rest of the children of the Monarch were styled Prince or Princess. Ever since the deposition of the Targaryens during Robert's Rebellion, the title "Prince of Dragonstone" has not been used; the children of the monarch are referred to only as Prince or Princess.
In Dorne, the ruler of is styled Prince of Dorne, following the tradition of the Rhoynar immigrants, imposed by Nymeria during the unification of the region under House Martell. The offspring of the Prince are also styled "Prince" or "Princess", as we can see with Oberyn Martell and the children of Prince Doran Martell.
Some of the rulers of the Summer Islands, like Jalabhar Xho, style themselves "Princes." 
- Prince of Dragonstone
- Prince of Summerhall
- Prince of Dorne
- Prince of Pentos
- Princes of Lorath
- Prince of Winterfell
- Prince of Chroyane
- Prince of Ny Sar
- ↑ 1.0 1.1 The World of Ice & Fire, Ancient History: Ten Thousand Ships.
- ↑ A Dance with Dragons, Chapter 1, Tyrion I.
- ↑ The World of Ice & Fire, The Free Cities: Lorath.
- ↑ The World of Ice & Fire, The Targaryen Kings: Aenys I.
- ↑ The Sons of the Dragon.
- ↑ The World of Ice & Fire, The Targaryen Kings: Daeron II.
- ↑ The World of Ice & Fire, The Summer Isles.