The aging of the population is the most consequential epidemiologic event of our times. The whole societal organization, including medicine and public health, needs to accommodate the evolving demographic landscape, and to focus on the management of chronic diseases, disability, and functional dependence, as well as on the most effective utilization of limited resources.

The management of an aging society is based on the twofold hypothesis that death cannot be indefinitely postponed, but disease and functional decline may be delayed until the latest stages of life. “Compression of morbidity” is the main goal of geriatric medicine, and it involves rehabilitation and provision of a supportive environment where the elder is able to thrive, in addition to medical care and disease prevention. The achievement of this goal implies the ability to define aging, and to estimate the risk of aging-related events such as death, disease, and disability, as well as the reversibility of this risk.

Perhaps the most complete definition holds aging as “loss of entropy” and “loss of fractality.” Loss of entropy implies a progressive decline in functional reserve of multiple organs and systems, and consequently reduced tolerance of stress, loss of fractality a progressive decline in the ability to coordinate different activities and to negotiate the environment.