Telomeres, located at the ends of eukaryotic chromosomes, are DNA extensions consisting of guanine-rich tandem TTAGGG amino acid sequences. The six telomere-specific proteins TERF1/TRF1, TERF2/TRF2, POT1, TINF2/TIN2, TPP1, TERF2IP/RAP1 are called shelterin complex proteins. All shelterin subunits combine with this sequence to form a complex and contribute to telomere stability. Changes in the structure or function of any of the shelterin proteins can lead to the generation of unwanted DNA damage responses and thus cellular senescence and death. In this chapter, telomere structure, the structure and function of shelterin complex proteins and their relationship with disease will be analysed with the help of studies.