The liver plays a key role in the metabolism of nutrients. Therefore, liver failure is often associated with malnutrition. It is well-established that malnutrition is an independent prognostic factor in patients with cirrhosis and liver failure. Since standard anthropometric and biological indexes are associated with liver dysfunction, nutritional assessment is difficult in patients with cirrhosis. In this review, we explain the various causes and mechanisms leading to malnutrition in cirrhosis. We also describe reliable methods used to assess the nutritional condition of these patients. Finally, we stress the importance of nutritional care in cirrhosis and liver dysfunction, describing its specific characteristics and indications.