Introduction James H. Hull 1,2 and Jemma Haines3,4,5 1 Respiratory Medicine, Royal Brompton Hospital, London, UK. 2 Institute of Sport, Exercise and Health, University College London, London, UK. 3 Faculty of Biology, Medicine and Health, School of Biological Sciences, Division of Infection, Immunity &Respiratory Medicine, The University of Manchester and Manchester Academic Health Science Centre, Manchester, UK. 4 NIHR Manchester Biomedical Research Unit, Manchester, UK. 5 Manchester University NHS Foundation Trust, Manchester, UK Corresponding author: James H. Hull (J.Hull@rbht.nhs.uk) @ERSpublications This Monograph provides a comprehensive guide to the assessment and management of individuals presenting with seemingly “unexplained” or complex respiratory symptoms, which are frequently overlooked and often associated with significant patient morbidity https://bit.ly/3HbXEs6 Copyright ©ERS 2022. Print ISBN: 978-1-84984-151-1. Online ISBN: 978-1-84984-152-8. Print ISSN: 2312-508X. Online ISSN: 2312-5098. Breathlessness is the key presenting symptom in many heart or lung diseases and thus its presence mandates a systematic and thorough search for any underlying pathological cause. In a proportion of individuals, however, despite extensive investigation, the origin and aetiology of their breathlessness may remain unclear or appear disproportionate to any underlying condition that is identified. In this context, the term “complex breathlessness” may be applied. The assessment and management of complex breathlessness is challenging both from the patient’s and the clinician’s perspective. For patients suffering with this issue, there are usually three main concerns: 1) the need to be satisfied that no pathological explanation has been overlooked 2) to obtain acknowledgement of the impact of symptoms and 3) to be reassured that there is a logical approach to their treatment. The overall aim of this Monograph is therefore to provide clinicians at all levels with a comprehensive guide to the assessment and management of individuals presenting with seemingly “unexplained” or complex breathlessness. Its 15 chapters cover all aspects needed to assess and successfully manage this challenging clinical scenario, providing clinicians with a useful reference when faced with a symptomatic breathless patient with no obvious underlying cause or with disproportionate symptoms. Specifically, the Monograph acts to highlight several potentially less commonly considered clinical entities and their associated features, to ensure that they are not overlooked. Secondly, it considers the symptom of breathlessness and how to approach its management, potentially in the absence of a clear diagnosis or set of abnormalities on investigation. The introductory chapters provide the reader with a solid foundation from which to better understand the context of complex breathlessness. The epidemiology of breathlessness is considered in chapter 1, which explores persistent breathlessness symptom prevalence across x https://doi.org/10.1183/2312508X.10015522