Telomerase is a unique ribonucleoprotein reverse transcriptase that uses an integral RNA template to catalyze the addition of telomeric repeats at telomeres. This mechanism is required for the maintenance of chromosome termini, as the structure and integrity of telomeres are essential for genome stability. Although the catalytic subunit of the enzyme shares several features with other reverse transcriptases, it differs in having telomerase-specific structures and functions. Structurally, the telomerase reverse transcriptase protein component contains unique am ino-and carboxy-terminal domains that flank centrally-located reverse transcriptase motifs. Functionally, unlike reverse transcriptases, telomerase contains an integral RNA component and is able to synthesize telomeric repeats. Here we discuss the evolutionary relationship of telomerase to other nucleic acid polymerases and reverse transcriptases and the various functions that regulate the elongation of chromosome ends. Such functions include interaction with the DNA substrate, nucleolytic activity, multimerization and processivity. In addition, we propose telomere-lengthening independent functions ascribed to telomerase.