Telomerase is a ribonucleoprotein enzyme that catalyses the cellular synthesis of telomeric DNA during cellular division, resulting in maintenance of telomere length and increased proliferative potential. Several studies suggest that the telomerase may play an important role in the diagnosis and prognosis of cancer because its expression strongly correlates with the potential tumour progression. Ninety percent of human cancers on different organs have shown high telomerasa activity. This book reviews research in the field of telomerase including functions of telomerase independent of its interaction with telomeres on gene expression and chromatin structure; histone deacetylase inhibition as an anticancer telomerase-targeting strategy and others.