Telomeres provide an essential 'capping' function, which prevents the natural end of a chromosome from being recognised as a simple dsDNA break. The biology of human telomeres is inextricably linked with both cancer and ageing. As such there is considerable interest in determining the length of these essential and dynamic structures. Here I review, from the standpoint of ageing research in humans, the current situation with regards to technologies available to determine telomere length in human cells and tissues.