Chronic Respiratory Failure (CRF) develops very frequently in the late stage of Chronic Obstructive Pulmonary Disease (COPD). At present, only long term oxygen-therapy (LTOT) is a recognised treatment able to significantly improve survival in chronically hypoxaemic COPD patients. Although long-term non invasive ventilation (NIV) is widely accepted for the treatment of chronic hypercapnia due to restrictive thoracic or neuromuscular diseases its use in stable hypercapnic COPD patients is still discussed. Four potential mechanisms explaining the effectiveness of NIV, as applied by positive pressure (NIV), in these patients rely to: 1) unloading respiratory muscles, 2) improvement of sleep quality and correction of hypoventilation, 3) “resetting” of respiratory centers, and 4) cardiovascular effects. In hypercapnic COPD, home NIV was associated to longer survival as compared with standard care when it was targeted to maximise reduction of hypercapnia, or in patients being discharged after acute on CRF. Despite the ability to improve gas exchange and health related quality of life, and to reduce readmissions, the generalized use of NIV in hypercapnic stable COPD still remain questionable. International documents provide indications for NIV prescription in COPD. Presence of nocturnal hypoventilation, sleep fragmentation and multiple acute exacerbations per/year are considered the optimal indication for home NIV in these patients, in particular when a progressive deterioration of clinical conditions and instability of the respiratory function are reported.