Rationale: Application of long-term non-invasive ventilation (NIV) in chronic obstructive pulmonary disease (COPD) patients with chronic hypercapnic respiratory failure (CHRF) has recently been shown to improve outcomes. However, the mechanism behind these improvements are unknown. We hypothesize that NIV stabilizes FEV1 via beneficial effects on inflammation and repair pathways in patients with COPD. In the present study we aim to investigate, in COPD patients with CHRF, 1. change in FEV1 after 3 months nocturnal NIV in stable hypercapnic COPD patients as compared to standard care 2. the relationship between FEV1 change and modification of systemic and airway inflammation and remodelling, lung hyperinflation, and airway morphology. 3. predictors of a favourable response to chronic NIV in COPD patients with CHRF. Study design: multicentre randomised controlled study investigating the effects of NIV on airway morphology, airway inflammation and remodelling in hypercapnic COPD patients including a control group that will postpone the initiation of NIV for 3 months. In addition we will investigate how patient demographics, patient and disease characteristics and systemic and airway inflammation predict the response to chronic NIV in severe stable COPD. To do this, all patients will be followed for 6 months after NIV initiation. Main study parameters/endpoints: The main endpoint is the change FEV1 after 3 months. Furthermore, as we recognise that FEV1 might not be the most important patient-related outcome, we will assess which parameters affect health-related quality of life after 3 and 6 months.