Aging is associated with progressive increase in body fat and a corresponding decline in lean muscle mass. When the decrease in muscle mass reaches a critical threshold, this may affect muscle strength and consequently limit the ability to cope with the activities of daily living, reducing the independence of elders. It is widely accepted to define sarcopenia as the loss of skeletal muscle mass and strength that occurs with advancing age. It is more difficult to establish cut-off points which are clinically relevant. The purpose of this paper is to summarize the definitions of sarcopenia and the assessment tools that can be used in clinical practice.