Duke of Valentinois is a title of nobility, originally in the French peerage. It is currently one of the many hereditary titles claimed by the Prince of Monaco despite its extinction in French law in 1949. Though it originally indicated administrative control of the Duchy of Valentinois, based around the city of Valence, the duchy has since become part of France, making the title simply one of courtesy.

The sovereign prince is the monarch and head of state of the Principality of Monaco. All reigning princes and princesses have taken the name of the House of Grimaldi. When Prince Rainier III died in 2005, he was Europe's longest reigning monarch. The Grimaldi family, which has ruled Monaco for eight centuries, is Europe's longest-ruling royal family.