Boso (French: Boson; c. 841 – 11 January 887) was a Frankish nobleman of the Bosonid family who was related to the Carolingian dynasty[1] and who rose to become King of Lower Burgundy and Provence.

In 872, Charles appointed him chamberlain and magister ostiariorum (master of porters) to his heir Louis the Stammerer.

Louis was reigning as a subordinate king of Aquitaine, but because of his youth[clarification needed], it was Boso who looked after the administration of that realm.

In the autumn of 875, Boso accompanied Charles on his first Italian campaign and at the diet of Pavia in February 876 he was appointed arch-minister and missus dominicus for Italy and elevated to the rank of duke.

On 15 October 879, the bishops and nobles of the region around the Rhône and Saône rivers assembled in the Synod of Mantaille.

Boso's realm, usually called the Kingdom of Provence, comprised the ecclesiastical provinces of the archbishops of Arles, Aix, Vienne, Lyon (without Langres), and probably Besançon, and the dioceses of Tarentaise, Uzès, and Viviers.

In August 882, Boso was again besieged at Vienne by his brother, Richard the Justiciar, duke of Burgundy and count of Autun, who took the city in September.