The fundamental problem that dividing cells have to ov- come is that of end-replication. Chromosomes shorten by many bases during DNA replication and so this presents a major hurdle that a cell has to overcome both to enable it to proliferate and for the larger organism to survive and reproduce. The enzyme telomerase provides a mechanism to ensure chromosome stability in both normal and neoplastic cells. The demonstration of telomerase expression in a majority of tumors and the realization of the potential role of telomerase in aging has opened up the potential for telomerase to be used as a target for therapeutic intervention. There is therefore great interest in the expression and activity of telomerase in a wide range of biological disciplines. Telomeres and Telomerase: Methods and Protocols has been produced as a tool for the many researchers in different areas of cell biology who are interested in following research in the area of telomerase and telomere maintenance, either in the area of fundamental mec- nisms or perhaps in the area of more applied drug discovery work.