This study is being done to better understand how well the medication mepolizumab (NUCALA) is working in routine medical practice to treat a sub-population of adult patients with severe asthma who have what is termed an eosinophilic phenotype (SA-EP). Participants will come to the clinic for regular scheduled visits as decided with the doctor and also at specified timepoints (enrollment in the study, 6 months, 12 months, and 24 months after enrollment). At visits, participants will be asked to complete questionnaires about their asthma and its impact on their life as well as, at some visits, to do breathing tests by blowing into equipment to measure their lung function. Taking part in this research will last up to 24 months. 

1. Inclusion
   1. Adults aged 18 years or over
   2. Participant has a confirmed asthma diagnosis with physician decision to initiate treatment with NUCALA
   3. Participants with ≥60% predicted FEV1 and ≤4 exacerbations per year, as confirmed by the physician
   4. Written informed consent
2. Exclusion
   1. Investigator concerns about participant’s willingness to adhere to biologic treatment for any reason (e.g., cost, behavior, difficulty with access to healthcare)
   2. Any NUCALA use in the 6 months prior to enrollment
   3. Participants currently on mOCS or intramuscular corticosteroids
   4. Participants using omalizumab, reslizumab, dupilumab, tezepelumab, or benralizumab within the 6 months prior to enrollment
   5. Participating in an interventional study with a treatment intervention
   6. Other clinically significant respiratory conditions (e.g., bronchiectasis, pulmonary fibrosis)
   7. Current smokers