Jack William Szostak (London, November 9, 1952) is an Anglo-American biologist who was raised in Canada. Szostak is Professor of Genetics at Harvard Medical School. He shared the Nobel Prize in Physiology or Medicine in 2009 for the discovery of how chromosomes are protected by telomeres. His co-winners were Elizabeth Blackburn and Carol Greider. Szostak is also credited with the construction of the world's first yeast artificial chromosome.