Telomeres are essential functional elements of eukaryotic chromosomes. Their fundamental biological role as protectors of chromosome stability was identified for the first time in the 1930s by Hermann Muller and Barbara McClintock based on pioneering cytological experiments. Modern molecular research carried out more recently revealed that telomeres and telomerase play important roles in processes such as carcinogenesis and cellular senescence. This special issue presents the most recent developments in this highly active field of research. It is becoming increasingly clear that molecular pathways involved in regulation of telomere length and structure are functionally linked with pathways involved in DNA damage response, cellular stress response, chromatin organization and perhaps even pathways that regulate evolutionary chromosome rearrangements. The above functional link is explored by the leading experts in the field of telomere biology. Cell biologists, molecular biologists, oncologists, gerontologists, and radiobiologists with an interest in the role of telomeres/telomerase will appreciate the up-to-date information in this publication.