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Severe asthma remains a condition in search of deeper understanding and of newer effective therapies. Risk factors for developing severe asthma, phenotyping of disease, characterizing the inflammatory response and understanding of poor therapeutic responses to corticosteroids are important areas of research. The development of biomarkers for phenotypic diagnosis and prognostic reasons is important.Severe asthma has been defined as asthma that does not respond adequately to asthma medications, particularly corticosteroids, with continuing loss of control of asthma and future risk of exacerbations and side effects from corticosteroid therapy. This is a heterogeneous condition and cluster analyses have yielded phenotypes on the basis of age of onset of disease, sex, lung function, atopy and questionnaire data. Use of sputum eosinophil counts has further defined a group with persistent eosinophilic inflammation despite corticosteroid therapy, and a noneosinophilic group with uncontrolled asthma.Use of a single biomarker provides value in phenotyping and in predicting response to treatment but many more biomarkers such as those derived from -omic approaches remain to be used in the analysis. A systems biology approach to finding novel biomarkers is the way forward to stratify severe asthma so that appropriate and distinct therapies can be selected for each subtype.