Sarcopenia is the age-associated loss of skeletal muscle mass and function. It is a major clinical problem for older people and research in understanding of pathogenesis, clinical consequences, management, and socioeconomic burden of this condition is growing exponentially. The causes of sarcopenia are multifactorial, including inflammation, insulin resistance, changing endocrine function, chronic diseases, nutritional deficiencies and low levels of physical activity. Operational definition of sarcopenia combines assessment of muscle mass, muscle strength and physical performance. The diagnosis of sarcopenia should be based on having a low appendicular fat free mass in combination with low handgrip strength or poor physical functioning. Imaging techniques used for estimating lean body mass are computed tomography, magnetic resonance imaging, bioelectrical impedance analysis and dual energy X-ray absorptiometry, the latter considered as the preferred method in research and clinical use.