This book is a comprehensive and up-to-date review and evaluation of the contemporary status of telomerase research.  Chapters in this volume cover the basic structure, mechanisms, and diversity of the essential and regulatory subunits of telomerase.  Other topics include telomerase biogenesis, transcriptional and post-translational regulation, off-telomere functions of telomerase and the role of telomerase in cellular senescence, aging and cancer. Its relationship to retrotransposons, a class of mobile genetic elements that shares similarities with telomerase and serves as telomeres in selected organisms, are also reviewed.