ERS | monograph Preface John R. Hurst It’s an exciting time to be an eosinophil biologist, or a healthcare professional caring for people with eosinophilic diseases. Leveraging a deeper scientific understanding of these enigmatic cells, we now have specific biological treatments that are transforming the management of rare and common (lung) diseases alike. As ever, this Monograph provides a state-of-the-art collection of reviews – here, covering the spectrum of eosinophilic lung diseases, including those with multisystem involvement. Given how quickly the field is moving, I congratulate the Guest Editors David J. Jackson and Michael E. Wechsler on delivering this excellent and timely collection. I would also like to extend my thanks to the chapter authors for their authoritative summaries. The scope of this book is broad, basing approaches to the management of eosinophilic lung diseases on a fundmantal understanding of eosinophil biology in health and disease. Important questions remain, not least around the safety of long-term eosinophil depletion, and there is still much to learn. The final chapter considers where future developments may lie. So without further preamble, I invite you to read on and benefit from this excellent collection. Disclosures: J.R. Hurst reports receiving grants, personal fees and non-financial support from pharmaceutical companies that make medicines to treat respiratory disease. This includes reimbursement for educational activities and advisory work, and support to attend meetings. Copyright ©ERS 2022. Print ISBN: 978-1-84984-142-9. Online ISBN: 978-1-84984-143-6. Print ISSN: 2312-508X. Online ISSN: 2312-5098. https://doi.org/10.1183/2312508X.10021621 v