Frailty is an end stage of aging, characterized by physical weakness, chronic inflammation, and lack of robustness in response to challenges. Frail individuals tend to spiral downward into organ failure and death in response to adverse circumstances, such as infection or injury, that less frail, younger individuals can survive. The question of how to reverse frailty is an important one; in principle, a good enough way of addressing the underlying causative mechanisms of aging would lead to improvement in patient outcomes. A number of the groups involved in development of first generation age-slowing and rejuvenating therapies are looking to frailty as a target for initial clinical trials.