ERS | monograph Preface Robert Bals CPET is one of the most useful and informative diagnostic approaches in pulmonary medicine. It offers deep insight into the cardiopulmonary network and generates data that can be used in diagnosis, staging and outcome prediction in multiple lung diseases. In the hands of an experienced investigator, exercise testing looks easy and elegant. For the patient, exercise testing focuses on relevant outcomes, such as exercise capacity and dyspnoea. It also has the benefit of being noninvasive. However, for novices in this area, the large amount of information generated and the task of interpreting this data can cause a sense of reluctance. The data that result from exercise testing differ in complexity, ranging from simple one-figure measurements to graphical displays of time curves requiring sophisticated interpretation of. As a result, a comprehensive summary of the methodology of CPET is urgently needed to ensure its more frequent use in clinical practice. This ERS Monograph is therefore timely as it provides the reader with a broad and detailed overview of the various CPET applications. The initial chapters summarise the technologies and standard techniques used. They are followed by sections about individual disease areas and a chapter on lung transplantation. Self-assessment cases have also been included in this book, a first for the ERS Monograph book series. We hope that our readers like this new feature and will find it useful. The Guest Editors Paolo Palange, Pierantonio Laveneziana, J. Alberto Neder and Susan A. Ward have worked very hard on topic selection and to integrate these aspects into a book that summarises current knowledge. Together with the authors, they have produced a practice-guideline publication that comprises both background information and hands-on application. I am sure this comprehensive review will be useful in the clinical practice of a broad range of respiratory physicians, and will improve patient care. Disclosures: R. Bals has received grants from the German Research Ministerium and the Deutsche Forschungsgemeinschaft. He has also received personal fees from GSK, AstraZeneca, Boehringer Ingelheim and CSL Behring. Copyright ©ERS 2018. Print ISBN: 978-1-84984-095-8. Online ISBN: 978-1-84984-096-5. Print ISSN: 2312-508X. Online ISSN: 2312-5098. https://doi.org/10.1183/2312508X.10017918 v