Carolyn Widney "Carol" Greider is an American molecular biologist who co-discovered the enzyme telomerase in 1984.

Her research on telomerase, an enzyme that replenishes the telomere to protect chromosomes from degradation, has been fundamental to understanding the mechanisms of aging and the development of cancer.

She was awarded the Nobel Prize in Physiology or Medicine in 2009 for this work.

Greider was a Daniel Nathans Professor and Director of Molecular Biology and Genetics at Johns Hopkins University.

She was elected as member of the European Academy of Engineering in 2015.