Cirrhosis represents the final stage of many chronic liver diseases and is associated to more or less pronounced hyponutrition, independently of the etiology, particularly at advanced stages. Its origin is multifactorial, with three factors contributing to it: a) limitation or decrease of intake; b) impairment in nutrients digestion or absorption; and c) the interference with nutrients metabolism. A poor nutritional status is associated with a poor survival prognosis. Whether caloric-protein malnourishment (CPM) is an independent predictor of mortality or only a marker of the severity of liver failure is subject to controversy. There is no consensus on which are the best diagnostic criteria for CPM in cirrhosis. Assessment of hyponutrition is extremely difficult since both the disease itself and the triggering or etiologic factors affect many of the parameters used. Metabolic impairments mimic a hypercatabolic state. These patients have decreased carbohydrate utilization and storage capacity and increased protein and fat catabolism leading to depletion of protein and lipid reserves. These abnormalities together with decreased nutrients intake and absorption are the bases for CPM. The most important metabolic impairment in patients with advanced liver disease is the change in amino acids metabolism. The plasma levels of branched amino acids (BAA) are decreased and of aromatic amino acids (AAA) are increased, which has therapeutic implications. Among the consequences of the structural impairments taking place in cirrhosis, we may highlight hepatic encephalopathy, defined as impaired central nervous system functioning that manifests as a series of neuropsychiatric, neuromuscular, and behavioral symptoms. These are due to the inability of the diseased liver to metabolize neurotoxins that accumulate in the brain affecting neurotransmitters and are attributed to the toxic effect of ammonium on the brain tissue. Nutritional therapy brings benefits in the different stages of the disease. In the short term, it improves nitrogen balance, decreases the hospital stay, and improves liver function. In the long term, it decreases the incidence and severity of encephalopathy and improves quality of life. Supplementation with enteral nutrition may improve protein intake, decrease the frequency of hospitalization, and improve the nutritional status, the immune function and the disease severity. Protein restriction is not indicated in compensated cirrhosis. A diet containing about 30 kcal/kg/d and 1.2 g of protein/kg/d is recommended. In acute encephalopathy temporary protein restriction may be needed, which should not last longer than 48 h and be minimized since even in patients with liver disease better outcomes are obtained without obtaining severe protein restriction. Oral supplementation with BAA slows the progression of liver disease and improves survival and quality of life. Supplementation should be done with fiber or diets with vegetable proteins, which bring high fiber content and less AAA, or either with dairy proteins in addition to a high ratio/nitrogen ratio.