Carolyn Widney Greider (born April 15, 1961) is an American molecular biologist and Nobel laureate. She is a Distinguished Professor of Molecular, Cell, and Developmental Biology at the University of California, Santa Cruz. Greider discovered the enzyme telomerase in 1984, while she was a graduate student of Elizabeth Blackburn at the University of California, Berkeley. Greider pioneered research on the structure of telomeres, the ends of the chromosomes. She was awarded the 2009 Nobel Prize for Physiology or Medicine, along with Blackburn and Jack W. Szostak, for their discovery that telomeres are protected from progressive shortening by the enzyme telomerase.