Buchau Abbey or the Imperial Abbey of Buchau (German: Reichsstift Buchau) was a nunnery, and later collegiate foundation, in the present town of Bad Buchau in Baden-Württemberg, Germany. According to its legend, it was founded in about 770 on an island in the Federsee by the Frankish Count Warin and his wife Adelindis (still commemorated in the local Adelindisfest). The nunnery was put on a secure financial footing by Louis the Pious, who in 819 granted the nuns property in the Saulgau and in Mengen. In 857, Louis the German declared it a private religious house of the Carolingian Imperial family and appointed as abbess his daughter Irmingard (died 16 July 866).