Sarcopenia, the age-associated loss of skeletal muscle mass and function, has considerable societal consequences for the development of frailty, disability, and health care planning. A group of geriatricians and scientists from academia and industry met in Rome, Italy, on November 18, 2009, to arrive at a consensus definition of sarcopenia. The current consensus definition was approved unanimously by the meeting participants and is as follows: Sarcopenia is defined as the age-associated loss of skeletal muscle mass and function. The causes of sarcopenia are multifactorial and can include disuse, altered endocrine function, chronic diseases, inflammation, insulin resistance, and nutritional deficiencies. Although cachexia may be a component of sarcopenia, the 2 conditions are not the same. The diagnosis of sarcopenia should be considered in all older patients who present with observed declines in physical function, strength, or overall health. Sarcopenia should specifically be considered in patients who are bedridden, cannot independently rise from a chair, or who have a measured gait speed less that 1 m/s^–1. Patients who meet these criteria should further undergo body composition assessment using dual energy x-ray absorptiometry (DXA) with sarcopenia being defined using currently validated definitions. A diagnosis of sarcopenia is consistent with a gait speed of less than 1 m·s⁻¹ and an objectively measured low muscle mass (eg, appendicular mass relative to ht² that is ≤ 7.23 kg/m² in men and ≤ 5.67 kg/m² in women). Sarcopenia is a highly prevalent condition in older persons that leads to disability, hospitalization, and death.