Malnutrition is reported in a significant percentage of COPD patients, and it may contribute to the onset of acute respiratory failure. Weight loss is due to the decrease of caloric support caused by breathlessness, digestive alterations due to hypoxemia and to the increase of energy expenditures caused by increased baseline requirements and diet induced thermogenesis (DIT). Malnutrition limits the ability to produce surfactant, leads to reduced protein synthesis, reduces cell mediated immune responses raising the patient's susceptibility to lung infection and affects the functioning of peripheral and respiratory muscles. The combination of malnutrition and COPD has devastating effects. Nutritional support is, therefore, an important part of therapy for the stable COPD outpatients, for hospital COPD patients and for ICU COPD patients. The nutritional program should follow an assessment of the nutritional status. With a correct number of calories and a correct composition of nutrients, it is possible to help these patients in the different clinical stages of the disease.