Physiology changes at the structural, functional, and molecular levels as people age, and every major organ system experiences physiologic change with time. The changes to the nervous system result mostly in cognitive impairments, the cardiovascular system develops higher blood pressures with lower cardiac output, the respiratory system undergoes a reduction of arterial oxyhemoglobin levels, the gastrointestinal system experiences delayed gastric emptying and reduction of hepatic metabolism, and the renal system experiences a diminished glomerular filtration rate. Combined, these changes create a complex physiologic condition. This unique physiology must be taken into consideration for geriatric patients undergoing general anesthesia.