Abstract : In 2004, a novel feature of neutrophil was discovered: their capacity to release Neutrophil Extracellular Traps or NETs. Since then, immunologists investigate these structures to unravel their functions in various diseases. In a first study, we demonstrated a main contribution of NETs, released by particular neutrophils, to allergic asthma onset triggered by three distinct pro-allergic environments in the mouse. In a second study, we observed NETs-enriched areas in lung biopsies of severe COVID-19 patients and characterized their locations. NETs were found in the airways, in the interstitium but also in blood vessels. These discoveries point out an important contribution of NETs to lung inflammatory diseases and suggest that NETs could be promising therapeutical targets in both allergic asthma prevention and in the severe forms of respiratory viral infections.