of pulmonary eosinophilia will ensure that the physician will not miss a key common eosinophil-related diagnosis [2]. Characterising eosinophilic patients is also critical to identifying what type of specific eosinophilic lung disease the patient has. The chapters on biomarkers [3] and imaging [4] help guide the physician through the challenges of establishing specific diagnoses. Once these key aspects of eosinophil biology, differential diagnosis and establishing a diagnosis are better appreciated, the reader is then ready to delve into the specifics of each of the eosinophilic disorders. From eosinophilic asthma [5] to eosinophilic COPD [6], from allergic fungal airway disease [7] to eosinophilic pneumonias [8], and from HESs [9] to EGPA [10], each chapter educates the reader about these specific disorders with regard to presentation, epidemiology, disease course and finally, treatment. The Monograph concludes with several important chapters that highlight the evolving complexity of eosinophils in the lungs [11–13]. What are the effects of eosinophils on the nerves? What role do eosinophils play in modulating immunity to respiratory viruses? What role do eosinophils play in driving autoimmune diseases? And what role do autoantibodies against eosinophils play in regulating tissue injury? Tissue damage Airway hyperresponsiveness Airway remodelling Mucus production Respiratory virus Allergen IL-33 IL-25 TSLP DC IL-13 IL-5 IL-3 IL-13 TGF-β MBP EPX IL-13 IL-5 EETosis (DNA, histones, MBP) IL-4 IL-4 ILC CD4+ T-cell B-cell Extracellular matrix Airway smooth muscle Platelet activation Thrombin activation Thrombus formation CLCs Eosinophil Figure 1. The multifaceted role of the eosinophil in eosinophilic lung diseases. DC: dendritic cell. Figure created using BioRender.com. https://doi.org/10.1183/2312508X.10021521 ix