Under a normal state, the extremities of chromosomes, telomeres, are protected against undesired fusion events. Alterations of the telomere structure are associated with genetic instability, while erosion of the telomeric repeats, occurring at each cell division, provides a mechanism controlling the long-term proliferation of somatic cells. Although the structure and composition of the human telomerase enzyme are now well characterized, the protein partners regulating the stability and conformation of its DNA substrate, the telomeric end, are much less known. A functional link has been recently evidenced between proteins that bind the double-stranded telomere repeats and those recruited at the 3' G-rich telomeric overhang. This review presents an update on these telomeric factors controlling telomere lengthening and discuss the actual models proposed for its regulation.