After the war, thousands of artworks that had fallen into enemy hands were found in Germany and brought back to the Netherlands. A proportion of these works are still being managed by the Dutch State. This collection is known as the NK Collection. Between 1998 and 2005, the Origins Unknown Agency has investigated the provenance of the objects in the collection, which originally numbered nearly 5000. These data are published on the ‘Origins Unknown’ website.

Thousands of artworks have never been recovered by the Netherlands Art Property Foundation. Information on part of this group of works has also been published on the website in 2016.

Since 1 September 2018, the ‘Origins Unknown’ website managed by the NIOD’s Expert Centre Restitution.