Severe influenza is defined as influenza with a severe symptom or syndrome such as respiratory distress or deceased consciousness or accompanying a severe complication such as encephalopathy or renal failure. In contrast to mild influenza, for which patients recover mostly by ambulatory care, severe influenza requires hospital admission in most cases or intensive treatment in the intensive care unit in some cases. In particular, the elderly, infants, and chronic patients are known to be at high risk for severe influenza because they may have accompanying complications such as exacerbation of an underlying disease, development of pneumonia, and another organ dysfunction or they may die. Therefore, there is an increasing need for an effective treatment method applicable to severe influenza. Severe influenza treatment methods, which have been recently discussed, include high-dose, long-term antiviral therapy, combination antiviral therapy, administration of antibiotics, application of extracorporeal membrane oxygenation (ECMO), administration of a corticosteroid, administration of intravenous immunoglobulin (IVIG), application of plasmapheresis, and administration of a statin. However, no comprehensive, specific expert guideline for these methods is available yet. The Transgovernmental Enterprise for Pandemic Influenza in Korea published in 2012 a guideline for the use of an antiviral agent for seasonal influenza. But the guideline deals with only the use of an antiviral agent, not the various treatment methods which can be applied to severe influenza [1]. Therefore, this guideline was developed by analyzing and evaluating domestic and international literature and guidelines with respect to the various treatment methods so that severe influenza could be effectively treated.