Aging is a complex developmental process that is, as yet, poorly understood. From a physical perspective, aging
involves a loss of resilience or reserve capacity to respond to stressors, and this acquired vulnerability usually
means that aging is associated with some greater susceptibility to illness as well as some decline in function over
time. Nevertheless, the effects of aging are highly variable; some men and women are still running races at the age
of 82, while others are frail and bed‐bound in a nursing home. In this brief overview, the physiology of aging in the
major organ systems, what is known about the human life span, and different theories of aging are outlined.