AbstractObesity Hypoventilation Syndrome (OHS) is defined as a combination of obesity (BMI > 30 kg/m2), daytime hypercapnia (PaCO2≥ 45 mmHg) and sleep‐disordered breathing after ruling out other disorders that may cause alveolar hypoventilation. Through the prism of the International Classification of Functioning, OHS is a chronic condition associated with respiratory, metabolic, hormonal and cardiovascular impairments, leading to a decrease in daily life activities, a lack of social participation and high risk of hospitalization and death. Despite its severity, OHS is largely underdiagnosed and the health‐related costs are higher than those of apneic or obese eucapnic patients. The present review discusses the definition, epidemiology, physiopathology and treatment modalities of ...