From a chronological viewpoint, medical treatment of the elderly (geriatrics) starts from the age of 65 years old. This definition per se is nowadays certainly not really an adequate definition of an elderly patient and the reason to be treated by a geriatrician. In addition to chronological age, other factors must be considered in order to define the elderly patient. Functional reserves decrease with age, which leads to increased vulnerability. Frailty as a term describes this situation and can be defined pathophysiologically by a mainly subclinical inflammatory state. Therefore, in 2007 the German Society of Geriatrics (DGG), the German Society of Gerontology and Geriatrics (DGGG), and the German Group of Geriatric Institutions (BAG) have jointly developed a definition of the geriatric patient.