Alfred Flechtheim was one of the most important art dealers of his era. His galleries included works by Paul Klee and Pablo Picasso. Persecuted by the Nazi regime, Flechtheim fled abroad. The fate of much of his collection remains obscure and a matter of contention to this day. In this study, experts from various disciplines use the example of Flechtheim to address controversial questions about the restitution of plundered art.