Throughout the world, there are many works of art that have a contested provenance. This may be due to theft, lost documentation, looting, or just information lost to antiquity. In some cases, just the previous or current ownership of the work is disputed, but in other cases the authenticity of the work itself may be thought to be a forgery. During World War II, Nazis stole many works of art from Jewish families, or looted them from cities in the war.