Roi fainéant is a French language phrase meaning "do-nothing king". It is primarily used to refer to the later kings of the Merovingian and Carolingian dynasties, after they seemed to have lost their initial energy. They were considered "useless" by Carolingian and even early modern historians, though current historical opinion is more nuanced.

Sigebert III is sometimes accredited the first roi fainéant of the Merovingian dynasty. The last Carolingians' effective rule was often limited to the region around Laon and they were sometimes derisively referred to as "Kings of Laon". Louis V of France was nicknamed le Fainéant ("the Do-Nothing"). The following kings are sometimes alleged to have been "do-nothings":

• Clovis III
• Clovis IV
• Chlothar III
• Chlothar IV
• Theuderic III
• Theuderic IV