Sarcopenia is a condition that is characterized by loss of muscle mass, muscle strength and muscle functional impairment with ageing. The definition of sarcopenia has been through various permutations; however, an enormous recent breakthrough is the inclusion of the condition in the ICD-10 classification of diseases. This chapter covers the background issues regarding definition before describing the epidemiology of the disease according to human and environmental factors. It then provides a practical guide for the assessment of sarcopenia in a clinical setting and finishes with advice on present treatment and the exciting frontiers of future therapies.