The Guelph Treasure is one of the most important collections of medieval German ecclesiastical art, named after the princely House of Guelph.
The collection of objects now known as the Guelph Treasure ("Welfenschatz") was part of the reliquary treasure at what today is known as Brunswick Cathedral. It came into the possession of the princely House of Guelph in 1671, which sold the 82 objects to a consortium of art dealers in 1929. Museums in the US, Sweden and Germany own some of the artwork today, as does the Prussian Cultural Heritage Foundation institution. Under the German Act to Protect German Cultural Property against Removal, removing the pieces of the collection from Germany, even for an exhibition, is only possible with authorization of the federal government's commissioner for Culture and Media. Descendants of Jewish art dealers have filed a case in a US court that calls for the return of the Guelph Treasure to heirs of the former owners.