Lastly, given the increasing use of novel therapies that target IL-5 or its receptor, effectively reducing, or even eliminating blood eosinophils, we address the safety and impact of eosinophil depletion, particularly in the context of their purported important regulatory and homeostatic roles [14]. Our Monograph culminates with a final review of the future prospects of translational and clinical eosinophil research, including a review of eosinophil subsets and the impact of recent developments in spatial and single-cell transcriptomics [15]. Given the rapid advances in our understanding of eosinophil biology and the increased prevalence of eosinophilic lung diseases, as well as the appreciation of their morbidity, our goal is to provide an accessible one-stop compendium for those who want to engage in advanced learning about eosinophilic lung diseases. That being said, we recognise that our knowledge about eosinophils continues to evolve and that new therapies and treatment strategies will be developed. Our Monograph will provide the reader with the requisite background, knowledge and understanding to better appreciate the advances that will be coming in the near future, and how to apply them to all patients with eosinophilic lung diseases. We extend our immense thanks to the authors of these chapters, who have done a stellar job. The authorship includes both world-leading authorities and up-and-coming stars in the field. We have convened a mixture of healthcare professionals and scientists, from around the world, and this has brought a diversity to the Monograph that is appropriate, given the global nature of the problems of eosinophilic lung diseases. We are grateful to the all the expert reviewers who gave up so much of their time to help us. We are particularly grateful to our authors and reviewers as the Monograph was compiled during the COVID-19 pandemic – their efforts during such a challenging time are greatly appreciated. We would also like to thank the ERS Monograph team, and particularly John R. Hurst (Editor in Chief), Rachel Gozzard (ERS Monograph Managing Editor) and Caroline Ashford-Bentley (ERS Editorial and Library Services Coordinator). We have really enjoyed bringing this Monograph to together and we sincerely hope you will find the chapters as useful and interesting as we did. References 1. Ackerman SJ. An introduction to eosinophils and their biology. In: Jackson DJ, Wechsler ME, eds. Eosinophilic Lung Diseases (ERS Monograph). Sheffield, European Respiratory Society, 2022 pp. 1–18. 2. Piggott LM, Gill CM, Kent BD. Differential diagnosis of pulmonary eosinophilia. In: Jackson DJ, Wechsler ME, eds. Eosinophilic Lung Diseases (ERS Monograph). Sheffield, European Respiratory Society, 2022 pp. 19–36. 3. Porsbjerg C, Björnsdóttir U. Biomarkers of eosinophilic inflammation. In: Jackson DJ, Wechsler ME, eds. Eosinophilic Lung Diseases (ERS Monograph). Sheffield, European Respiratory Society, 2022 pp. 37–50. 4. Bell A, Siddiqui S. Imaging. In: Jackson DJ, Wechsler ME, eds. Eosinophilic Lung Diseases (ERS Monograph). Sheffield, European Respiratory Society, 2022 pp. 51–72. 5. Rupani H, Gates J, Kavanagh JE, et al. Eosinophilic asthma. In: Jackson DJ, Wechsler ME, eds. Eosinophilic Lung Diseases (ERS Monograph). Sheffield, European Respiratory Society, 2022 pp. 73–99. 6. Karakioulaki M, Stolz D. Eosinophilic COPD. In: Jackson DJ, Wechsler ME, eds. Eosinophilic Lung Diseases (ERS Monograph). Sheffield, European Respiratory Society, 2022 pp. 100–118. 7. Ueki S, Fukutomi Y, Miyabe Y, et al. Allergic fungal diseases in the upper and lower airways. In: Jackson DJ, Wechsler ME, eds. Eosinophilic Lung Diseases (ERS Monograph). Sheffield, European Respiratory Society, 2022 pp. 119–140. 8. Gadre A, Akuthota P. Eosinophilic pneumonias. In: Jackson DJ, Wechsler ME, eds. Eosinophilic Lung Diseases (ERS Monograph). Sheffield, European Respiratory Society, 2022 pp. 141–152. x https://doi.org/10.1183/2312508X.10021521