Kassow was a consultant to the Museum of History of the Polish Jews, which opened on the site of the Warsaw Ghetto, and was responsible for two of the eight core exhibitions.
Rediscovering a Hidden Archive From the Warsaw Ghetto, Kassow speaks about the importance of preserving historical documents and the past.
His main focus is the Ringelblum Archive created in absolute secrecy by a small group of people that lived in the Warsaw Ghetto which were uncovered and studied about ten years later.
[7] In 2014, Indiana University Press and the United States Holocaust Museum published The Clandestine History of the Kovno Jewish Ghetto Police, with an introduction by Kassow.
His 2007 book Who Will Write Our History was adapted into a documentary film of the same title, directed by Roberta Grossman and produced by Nancy Spielberg.