Diplomatic action has been undertaken by the German Government, the City of Koblenz, and Kiefer himself, to secure the return of the pieces, which include the monumental work Pasiphae.

Directly after World War II, in May 1946, Haubrich presented the city with his Expressionism collection (Erich Heckel, Karl Schmidt-Rottluff, Ernst Ludwig Kirchner, August Macke, Otto Mueller) and works by other representatives of Classical Modernism (Marc Chagall, Otto Dix).

The second integral part of the museum is the Sammlung Ludwig, a collection of art by Picasso, Russian avant-garde and American Pop-art artists.

Peter Ludwig and his wife Irene later put their collection of the Russian avant-garde on permanent loan to the museum, including 600 works from the period 1905 to 1935 by artists such as Kasimir Malevich, Ljubov Popova, Natalia Goncharova, Mikhail Larionov, and Alexander Rodchenko.

The Wolfgang Hahn Prize has been awarded to the following artists: In 1999 the museum returned the painting Zwei weibliche Halbakte (Two Female Nudes ) (1919) by Otto Mueller to the heirs of Dr. Ismar Littmann.

[19] In February 2000 the museum returned La Grappe de Raisins (1920) by Louis Marcoussis (1883–1941) to the family of El Lissitzky and Sophie Lissitzky-Küppers.

[19] In 2013 the city of Cologne agreed that the Ludwig Museum should restitute six valuable drawings looted by the Nazis from the Jewish art collector Alfred Flechtheim to his heirs.