aspects of the respiratory microbiome in a range of different contexts: the paediatric microbiome and how this develops [5] viruses [6] and fungi [7] as part of the microbiome in addition to the more frequently studied bacteria. We move on to explore the respiratory microbiome in asthma and COPD [8], chronic suppurative lung diseases [9], interstitial lung diseases [10], acquired pneumonia [11], transplantation, cancer and HIV [12], and the interaction of the respiratory microbiome and the environment [13]. We invite readers to compare and contrast the findings in each area, because although individuality is a feature of host-associated microbial communities, common threads can be found in each. There are now many active researchers in the field, with different insights into the various aspects of the respiratory microbiome, and this is an excellent time to take stock of how it might develop and have an impact on research and clinical approaches to reducing disease. We thank our authors and our expert reviewers for their work on this Monograph, which include amongst them early career and senior authors from many leading groups in the field. Here we have attempted to collate and underline their achievements, highlight those of other researchers, while informing those new to the field about the current state of the art. References 1. Dickson RP, Cox MJ. Sampling. In: Cox MJ, Ege MJ, von Mutius E, eds. The Lung Microbiome (ERS Monograph). Sheffield, European Respiratory Society, 2019 pp. 1–17. 2. Einarsson GG, Boutin S. Techniques: culture, identification and 16S rRNA gene sequencing. In: Cox MJ, Ege MJ, von Mutius E, eds. The Lung Microbiome (ERS Monograph). Sheffield, European Respiratory Society, 2019 pp. 18–34. 3. Charalampous T, Kay GL, O’Grady J. Applying clinical metagenomics for the detection and characterisation of respiratory infections. In: Cox MJ, Ege MJ, von Mutius E, eds. The Lung Microbiome (ERS Monograph). Sheffield, European Respiratory Society, 2019 pp. 35–49. 4. Foesel BU, Pfeiffer S, Raj ACD, et al. Applying ecological theories in research: lessons learned from microbial ecology and evolution? In: Cox MJ, Ege MJ, von Mutius E, eds. The Lung Microbiome (ERS Monograph). Sheffield, European Respiratory Society, 2019 pp. 50–66. 5. de Koff EM, Pattaroni C, Marsland BJ, et al. The early-life microbiome: the key to respiratory health? In: Cox MJ, Ege MJ, von Mutius E, eds. The Lung Microbiome (ERS Monograph). Sheffield, European Respiratory Society, 2019 pp. 67–87. 6. Flight WG, Turkington CJR, Clokie MRJ. Viruses. In: Cox MJ, Ege MJ, von Mutius E, eds. The Lung Microbiome (ERS Monograph). Sheffield, European Respiratory Society, 2019 pp. 119–139. 7. Vandenborght L-E, Enaud R, Coron N, et al. From culturomics to metagenomics: the mycobiome in chronic respiratory diseases. In: Cox MJ, Ege MJ, von Mutius E, eds. The Lung Microbiome (ERS Monograph). Sheffield, European Respiratory Society, 2019 pp. 88–118. 8. Chung KF, Huffnagle GB, Huang YJ. Obstructive airways disease: potential pathogenetic roles. In: Cox MJ, Ege MJ, von Mutius E, eds. The Lung Microbiome (ERS Monograph). Sheffield, European Respiratory Society, 2019 pp. 140–157. 9. Rogers G, Huang YJ. Chronic suppurative lung disease: cystic fibrosis and non-cystic fibrosis bronchiectasis. In: Cox MJ, Ege MJ, von Mutius E, eds. The Lung Microbiome (ERS Monograph). Sheffield, European Respiratory Society, 2019 pp. 158–172. 10. O’Dwyer DN, Moore BB, Molyneaux PL. Interstitial lung disease. In: Cox MJ, Ege MJ, von Mutius E, eds. The Lung Microbiome (ERS Monograph). Sheffield, European Respiratory Society, 2019 pp. 173–187. 11. Bos LDJ, Rylance J, Gordon SB. The lung bacterial microbiome in community-acquired and nosocomial pneumonia. In: Cox MJ, Ege MJ, von Mutius E, eds. The Lung Microbiome (ERS Monograph). Sheffield, European Respiratory Society, 2019 pp. 188–194. 12. Bernasconi E, Aubert J-D, Koutsokera A, et al. Compromised immunity: transplantation, cancer and HIV. In: Cox MJ, Ege MJ, von Mutius E, eds. The Lung Microbiome (ERS Monograph). Sheffield, European Respiratory Society, 2019 pp. 195–215. x https://doi.org/10.1183/2312508X.10012119