ERS | monograph Preface Robert Bals US techniques are one of the most elegant diagnostic approaches in clinical medicine. In the hands of an experienced investigator, the US machine can provide deep insight into the physiology and pathology of the body. In most cases, US application is fast, radiation-free and does not cause pain. However, the outcome of the US examination depends largely on the capabilities and experience of the investigator. The development of medical US has an interesting history, further discussed in the Guest Ediors’ Introduction [1], with the abdomen and the heart being the major targets in recent decades. US-based diagnostics have also been introduced in the respiratory field. As elsewhere, the success of this method in the respiratory field is dependent on training and practice guidance in TUS, as well as the availability of a comprehensive text book. With this latter necessity in mind, we decided to fill this critical gap by devoting an ERS Monograph to the subject. This book provides the reader with a broad and detailed overview on the various application of TUS. The initial chapters summarise the technologies and standard approaches used. Subsequent chapters focus on specific diseases and cover additional areas such as cardiac US, application in children and US use during procedures. Thanks to the hard work of the book’s Guest Editors, Christian B. Laursen, Najib M. Rahman and Giovanni Volpicelli, readers of this Monograph will benefit from a book that provides a comprehensive overview of both the background and hands-on application of US. We hope that this important publication will not only aid the respiratory physician in their day-to-day practice but will also help generate more frequent use of TUS in the field. Copyright ©ERS 2018. Print ISBN: 978-1-84984-093-4. Online ISBN: 978-1-84984-094-1. Print ISSN: 2312-508X. Online ISSN: 2312-5098. https://doi.org/10.1183/2312508X.10001318 ix