The Cartier Ballon Bleu, launched in 2007, is a round watch whose crown is protected by a curved guard shaped like a ball, with a blue sapphire cabochon set in the crown. It was introduced in steel and in gold in several diameters, and sizes later covered roughly 33 to 44 mm; the 42 mm version carried the automatic calibre 1847 MC. The dial has Roman numerals and a blued-steel sword hand set, with the date window at 3 o’clock.

The rounded case with no sharp edges and the crown guard that appears to grow out of the case are the watch’s trademarks. The design reworked the Cartier round watch for a new generation, and it was later expanded into complications and skeleton versions.

The Ballon Bleu is considered one of Cartier’s modern successes, and the community sees it as an elegant daily dress watch with a recognisable signature, though some find the crown guard bulky. The original 2007 generation was later updated, and the Ballon Bleu de Cartier remains in the current collection.