NIH grantees Elizabeth H. Blackburn, Carol W. Greider, and Jack W. Szostak shared the 2009 Nobel Prize in physiology or medicine for their discovery of "how chromosomes are protected by telomeres and the enzyme telomerase." Like the plastic tips of shoelaces, telomeres protect chromosomes and the genetic information they contain. We now know that these chromosomal caps play critical roles in human health and disease.