Carolyn Widney Greider (born April 15, 1961) is an American molecular biologist and Nobel laureate.

Greider discovered the enzyme telomerase in 1984, while she was a graduate student of Elizabeth Blackburn at the University of California, Berkeley.

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.

[5] Greider is dyslexic and states that her "compensatory skills also played a role in my success as a scientist because one has to intuit many different things that are going on at the same time and apply those to a particular problem".

[8] Greider joined Blackburn's laboratory in April 1984 looking for the enzyme that was hypothesized to add extra DNA bases to the ends of chromosomes.

Blackburn and Greider looked for the enzyme in the model organism Tetrahymena thermophila, a fresh-water protozoan with a large number of telomeres.

[11] Greider's additional research to confirm her discovery was largely focused on identifying the mechanism that telomerase uses for elongation.

[32] Greider, Blackburn, and Szostak shared the 2006 Albert Lasker Award for Basic Medical Research for their work on telomeres,[33] before jointly receiving the Nobel Prize in 2009.

[34] Greider served as director of and professor at the Department of Molecular Biology and Genetics at Johns Hopkins Medicine.

[36] Greider's lab employs both student and post-doctoral trainees[37] to further examine the relationships between the biology of telomeres and their connection to disease.

[35] Greider's lab uses a variety of tools including yeast, mice, and biochemistry to look at progressive telomere shortening.