Carbohydrates and essentially glucose represent central energy sources of human metabolism, and some carbohydrates are precursors for synthetic pathways. Glucose is the standard carbohydrate in nutrition therapy of critically ill patients. In critical illness, carbohydrate metabolism becomes significantly impaired, mainly by inflammation-related insulin resistance. This is reflected by the phenomenon of stress-induced hyperglycemia. Blood glucose levels are routinely monitored in the intensive care unit (ICU), since it is recognized that disturbance severity of a variety of glucose metrics, including, but not limited to, glycemic variability, hyperglycemia, and hypoglycemia, is related to increased mortality in critically ill patients. Therefore, protocols for nutrition management and for prevention of hyper- and hypoglycemic episodes represent established treatment concepts in intensive care. This chapter will provide the reader with an up-to-date review of the literature and outline current concepts for the management of carbohydrate metabolism in critical illness.