Oxygen is the first-line therapy for hypoxemic respiratory failure and is usually delivered through nasal cannulae or a face mask. More recently, there has been increased interest in the use of high-flow nasal cannula (HFNC) oxygen therapy, in which optimally heated and humidified oxygen is delivered at high flow rates of up to 60 L/min. HFNC therapy has a number of advantages over traditional, low-flow oxygen therapy: provision of low-level positive-end expiratory pressure, flushing of anatomical dead space, provision of higher and more predictable fraction of inspired oxygen and enhanced patient tolerance and compliance. Much of the available evidence for its clinical utility comes from its use in neonatal and pediatric settings, but HFNC therapy has been studied in adults with acute hypoxemic respiratory failure, patients with chronic obstructive pulmonary disease and heart failure, and for preoxygenation before intubation, as well as postextubation to avoid or treat respiratory failure in high-risk groups. Currently, there are only a few high-quality studies evaluating outcomes of HFNC therapy in these patient groups, and a number of key questions remain to be answered, meaning that it is not possible to make strong recommendations regarding its use. Nevertheless, this is an exciting and innovative addition to the field of respiratory support for adult patients with a variety of respiratory pathologies.