Defining the signature and impact of lung HSCs. Lung HSCs have a bias toward megakaryopoiesis and erythropoiesis. They are also enriched for genes related to immune pathways and the maintenance of quiescence. The overwhelming majority of lung HSCs reside within the alveolar interstitium where gas exchange between inhaled air and the dense pulmonary capillary networks takes place. Several questions remain, highlighted in purple text, regarding the physiologic impact of lung HSCs. Do lung HSCs contribute directly to the lung megakaryocyte pool and in return support local HSC quiescence? What are the origins of lung HSCs? How and when are lung HSCs mobilized?