 De Montebello assisted in the formation of the Association of Art Museum Curators in 2001, and later helped forge its policy on spoliated World War II-era art, advocating transparent research into the ownership history of museum collections, and testifying on Capitol Hill.In August 2006 he successfully negotiated the precedent-setting agreement with the Italian government that ended years of disputes regarding the legal ownership of several works in its Greek and Roman collections.Under the terms of the historic pact, Italy provided long-term loans to the Met in exchange for the return of these works.