Asthma is a complex and heterogeneous disease. Patients experience wheezing, shortness of breath, and coughing, frequently occurring during the night or early morning. The condition is characterised by a range of clinical and pathogenic features including variable and recurring symptoms of airflow obstruction, bronchial hyperresponsiveness, mucus hypersecretion, and underlying pulmonary inflammation. The challenges are further exacerbated by the fact that symptoms of asthma can be non-specific and varied. This spectrum of causes and presentations can make the clinical development of new asthma treatments challenging.