ERS | monograph Introduction Kian Fan Chung1, Elliot Israel2 and Peter G. Gibson 3,4,5 @ERSpublications The comprehensive ERS Monograph on Severe Asthma provides an update on the latest advances and future plans for severe asthma http://bit.ly/2ZKA4N1 Severe asthma has now been recognised as a distinct form of asthma that responds poorly to currently available medications it is the asthma group with the greatest unmet need. Although the definition of severe asthma remains a pragmatic one, under this umbrella definition, there exist different phenotypes that can be distinguished on clinical presentation and natural history, and on certain biomarker features. In the last 10 years, substantial progress has been made in terms of understanding some of the mechanisms that drive severe asthma and with it, there has been the introduction of novel targeted therapies (particularly in the form of monoclonal antibodies that target components of the type 2 pathway) which are bringing therapeutic relief to a high number of patients with severe asthma. In the introduction to the ERS Monograph on Difficult-to-Treat Severe Asthma published 8 years ago, the editors pondered the most pertinent information that had emerged in the 10 years prior to the book’s publication, reflecting that: “the disease is heterogeneous, and the challenge for the next 10 years would be to understand the different types of severe asthma” [1]. In 2019, we can say that there have been significant advances in our understanding of the heterogeneous nature of severe asthma, such that new targeted treatments have been introduced for a particular phenotype of severe asthma: eosinophilic severe asthma. These advances have been made possible following the consensus agreement in 2014 on a definition of severe asthma that offers a pragmatic, bedside characterisation [2]. This basic stepping stone subsequently led to the description of clustering approaches that defined several clinical phenotypes from asthma cohorts around the world. More recently, a greater understanding of the mechanistic heterogeneity has been achieved through a precision medicine approach, with findings that have yet to be applied to the clinical problem. This Monograph is comprehensive in its coverage of all aspects of severe asthma, including its definition, evaluation, epidemiology, diagnosis, pathology, treatable traits, clinical and molecular phenotypes, mechanisms, treatment and management. It captures the progress Copyright ©ERS 2019. Print ISBN: 978-1-84984-103-0. Online ISBN: 978-1-84984-104-7. Print ISSN: 2312-508X. Online ISSN: 2312-5098. Correspondence: Kian Fan Chung, National Heart and Lung Institute, Imperial College London, Dovehouse Street, London SW3 6LY, UK. E-mail: f.chung@imperial.ac.uk 1 Experimental Studies Unit, National Heart and Lung Institute, and Data Science Institute, Imperial College London, London, UK. 2 Brigham & Women’s Hospital, Harvard Medical School, Boston, MA, USA. 3 Dept of Respiratory and Sleep Medicine, John Hunter Hospital, Newcastle, Australia. 4 Priority Research Centre for Healthy Lungs and Centre of Excellence in Severe Asthma, Faculty of Health and Medicine, The University of Newcastle, New Lambton Heights, Australia. 5 Hunter Medical Research Institute, Newcastle, Australia. https://doi.org/10.1183/2312508X.10019419 ix