The Guelph Treasure (German: Welfenschatz) is a collection of medieval ecclesiastical art originally housed at Brunswick Cathedral in Braunschweig, Germany. The Treasure takes its name from the princely House of Guelph (German: Welf) of Brunswick-Lüneburg.
In October 1929, the Treasure, consisting of 82 pieces, was sold by the former Duke of Brunswick to a consortium of Jewish art dealers. In 1935, in the Netherlands, they sold its major portion to agents of Hermann Göring, the second most powerful man in Nazi Germany.
After World War II, the art dealers' heirs unsuccessfully sought the restitution of the treasure. In Germany, the Limbach Commission, a government advisory body, found that there were no grounds for restitution, and in the U.S., the Supreme Court ruled in the 2021 case Germany v. Phillipp that the U.S. courts had no jurisdiction over the restitution claims.