Jacalyn M. Duffin CM FRSC (born 1950) is a Canadian medical historian and hematologist. She held the Hannah Chair, History of Medicine at Queen's University from 1988 until 2017. Formerly, she was President of the American Association for the History of Medicine and Canadian Society for the History of Medicine. From 1993–1995 she was Associate Dean Undergraduate Studies and Education at Queen's University. She is most well known for her testimony which led to the canonization of Marie-Marguerite d'Youville. As of 2010, she has published eight books (as author and editor) on the history of medicine and has written numerous articles on various subjects relating to the history of medicine, miracles, and hematology. In 2019, Duffin was inducted into the Canadian Medical Hall of Fame.