Leonard I. Zon, MD, is the Grousbeck Professor of Pediatrics at Harvard Medical School and Director of the Stem Cell Program at Boston Children’s Hospital, a Howard Hughes Medical Institute (HHMI) Investigator, and Professor of Stem Cell and Regenerative Biology at Harvard University. He is recognized internationally for his groundbreaking work in blood stem cell biology and cancer, and for pioneering the use of the zebrafish as an animal model for hematopoiesis and melanoma.