Severe asthma represents less than 5% of all asthma, but these patients are responsible for a disproportionate share of health care costs, morbidity and mortality associated with the disease. Severe problematic asthma corresponds to patients that fail to achieve asthma control despite being prescribed maximal therapies. This group is divided into severe difficult to control asthma and severe therapy resistant asthma. It is important to note this division as it leads to important differences in medical prognosis and therapy. Difficult to control asthma is the term used to describe children with significant ongoing symptoms that are due to underlying modifiable factors that, when addressed, lead to better control without increasing therapy intensity. On the other hand, therapy resistant asthma does not present modifiable factors, thus other treatments, including biological therapies, are justified.