Historical Documents:
Plunder of Art Treasures: Nizkor Org.
Nuremberg Trial: The Avalon Project
Atlantic Monthly Sept. 1946 & Oct. 1946
Documentation Project of Wartime Cultural Losses
NARA US National Archives Bibliography

Listings of Missing Art Works:
Czech Republic: Ministry of Interior
France: Catalogue des MNR
France: Schloss Collection
Germany: Lost Art Internet Database
Hungary: Art Restitution Project
Italy: Com. Interministeriale - Opere d'Arte
Lithuania: National Museum
Poland: Wartime Losses
Spain: Dispursed Art 1933-1945
Russia: Lost Art (no listings)
Russia: Displaced Cultural Valuables
Russia: Trophy Art

Museum Holdings:
Nazi-Era Provenance Internet Portal
Museum Provenance List
Netherlands: Origins Unknown
UK: Enemy Property (search)
Museum Policy: AAM
Museum Policy: ICOM 
Museum Policy: UK Provenance Research

Art Restitution Efforts:
Resources: U.S. Holocaust Museum
Art Loss Register (ALR)
Central Registry Looted Art
Commission for Looted Art in Europe (ECLA)
Commission for Art Recovery (WJC)
Getty Research Institute Library
HARP Holocaust Art Restitution Project
Holocaust Assets: US State Dept.
Looted Art - Research Catalog
Trans Art International (due diligence)
Legal Resources on the Spoils of War

News reports about looted art:
Museum Security Network W.W. II  Looting Information
THE ART NEWSPAPER - Looted Art
Arts Journal: Stolen Art