Oxygenation using High Flow Nasal Cannula (HFNC) was initially described in neonatal medicine, but, gradually, its use has extended to adult patients. The efficacy of the device has been linked to higher flows of oxygen delivered to the patients, air tract humidification, alveolar recruitment through a positive end-expiratory pressure (PEEP) effect, prevention of nasopharyngeal collapse, and dead-space washout. Beside the fact that HFNC is a non-invasive way of delivering oxygen to ICU patients, and is well tolerated, results from various clinical trials tend to show positive outcomes for patients presenting with acute hypoxemic respiratory failure (AHRF), during intubation, or during the post-extubation period. However, controversy arose from recent publications, and larger trials are still required to clarify the position of HFNC in the ICU, and help define the subgroups of patients presenting with AHRF that are most likely to benefit from HFNC therapy.