Severe asthma (SA) in an asthma that requires therapy with high dose inhaled corticosteroids with a second controller, or oral corticosteroids, to ensure that it does not become "uncontrolled," or that it does not respond to appropriate therapy. Severe asthma has a great impact on quality of life. There is a great heterogeneity of this disease, not only from a clinical point of view, but also from a functional and pathophysiological one. It is really hard to identify specific characteristics that identify this subgroup. Specific registers of SA, both national and international, are really important to describe the epidemiological characteristics of the disease and to analyze the clinical characteristics of the various subgroups of patients. This is an excellent starting point to be able to investigate the characteristics of the disease in detail.