This book provides a practical, stepwise, evidence-based approach to effective management of patients with difficult to treat asthma. The impact of asthma on morbidity and healthcare utilization increases exponentially with severity. Severe refractory asthma accounts for less than 5% of all asthma. Its prevalence, however, is often overestimated as there are several other confounding factors that make asthma difficult to treat . Many novel (albeit expensive) therapies are now available and providers caring for patients with severe asthma are charged with selecting the best evidence treatment. This calls for complex and nuanced decision-making. Whether people with asthma gain and maintain control over their condition depends not only on the availability of effective drugs, but also multiple patient and healthcare provider behaviors.