Dr Ratjen is the Division Chief of Paediatric Respiratory Medicine at the Hospital for Sick Children in Toronto. He serves as a Professor of Paediatrics at the University of Toronto, and Program Head and Senior Scientist at the Research Institute in the Department of Translational Medicine. Dr Ratjen holds the H.E. Sellers Chair in Cystic Fibrosis at the Hospital for Sick Children. His research interests include early intervention strategies in paediatric lung diseases and physiological tests to assess early lung disease, with a particular focus on cystic fibrosis lung disease. Dr Ratjen has conducted multiple clinical trials addressing various aspects of cystic fibrosis including the treatment of airway infections and airway inflammations as well as new therapeutic strategies.