In their 1985 Cell paper, Greider and Blackburn announced the discovery of an enzyme that extended the DNA at chromosome telomeres in the ciliate, Tetrahymena. Since then, there has been an explosion of knowledge about both the RNA and protein subunits of this unusual ribonucleoprotein enzyme in organisms ranging from the ciliates to yeast to humans. The regulation of telomerase is now understood to take place both at the level of synthesis of the enzyme and via the state of its substrate, the telomere itself. The roles of telomerase in both cellular immortality and cancer are vibrant areas of current research.