Despite advances in asthma therapy and worldwide distribution of asthma guidelines, a significant number of patients with asthma continue to experience poor control of their disease. This recalcitrant form of asthma is commonly referred to as severe or difficult-to-treat asthma and is characterized by corticosteroid insensitivity, with persistent lack of control despite corticosteroid therapy or worsening of asthma control on reduction or discontinuation of corticosteroid therapy. While poor asthma control is frequently attributed to poor adherence to prescribed medications and/or recommended environmental restrictions, 5 –10% of patients experience poor control because they suffer from an underlying severe asthma pathophysiology characterized by airway inflammation resistant to medical therapy.1 Although the population of patients with severe asthma is relatively small, this group deserves special focus because they account for a substantial portion of total asthma morbidity, mortality and cost. Until recently, few clinical studies were specifically designed to investigate the many other facets of treatment failure of patients with severe asthma, that include inhaler technique or which offer newer forms of treatment such as thermoplasty. In this context, the majority of the nine asthma-related articles within this issue directly or indirectly relate to the severe asthma phenotype and focus on these unexplored areas.

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