This study aims to prospectively assess the asthma control and management of asthma patients who are on step 4, 5 asthma of GINA in Hong Kong (on at least medium-dose ICS-LABA as controller therapy for asthma) and also observe their exacerbations over 2 years. In addition, this study will also assess patients who are on biologics for their suitability and outcome. The investigators hope this study will be able to provided data regarding the management and outcome of patients who have difficult-to-treat and severe asthma. The investigators plan to build a biologic registry for asthma that would be able to help local doctors to gain experience to the use of these new and expensive medications. This is a multi-centre study involving public hospitals in Hong Kong. This study is important as this will generate local data for healthcare planning for severe asthma in Hong Kong.