The recognition and implementation of personalized internal medicine is of the utmost importance for physicians, nurses, dieticians and other healthcare professionals engaged in clinics. The assessment of sarcopenia and frailty, in middle-aged patients, as an embodiment of treatment personalization, is essential in settings of acute and chronic disease, both in the hospital and in ambulatory settings. This book describes various practical tools for the assessment of sarcopenia and frailty, reviews relevant findings from the current professional literature, and suggests treatment modifications for frail patients.