Three key observations - the remarkable continuity of mortality improvement, the changing age pattern of mortality improvement, and the location of longevity extension potentials at the highest ages - are the basis for the individual articles of this thesis. The articles explore challenges that are caused by the interplay of the above mentioned developments. The proposed approaches, as well as the insights offered on the boundaries of age-specific mortality, shed light on some of the challenges both demographers and the general public face currently, and will face in the future.<eng>
