Mandel specializes in modern Jewish history and has focused particularly on the 20th-century French Jewish experience. She has written extensively on the impact of genocide on the reconstruction of community and on inter-ethnic relations. Her work has been marked by an on-going engagement with comparative historical methodology, and she has written extensively about Armenian and Muslim communities in France as well. She has published extensively on various topics, and teaches courses on many aspects of modern Jewish history, including history of the Holocaust, Zionism and the birth of the state of Israel, and history of American Jews.