Severe asthma is associated with substantial morbidity, use of healthcare resources, and long-term sequelae including declining lung function and frequent exacerbations. The identification of severe asthma is challenging due to the heterogeneity of the disease, the complexity of diagnosis, and the impact of comorbidities. A structured approach to the assessment of severe asthma may be helpful to the practicing clinician. First, it is important to confirm a diagnosis of asthma. The lack of a response to treatment or the requirement for high doses of medication to control symptoms are signs of disease mimickers, comorbidities, or the influence of environmental factors. Second, medication adherence and the inhaler technique should be checked in advance. Third, the phenotypic characteristics of patients confirmed to have severe asthma can indicate the therapies likely to be most effective. Further research that seeks to define the phenotypes of severe asthma based on endotype will enable the development of novel and effective therapeutic options for patients with severe asthma. (Korean J Med 2018;93:153-158)