Human airways are a paragon of intrinsic engineering. They experience 7,000-10,000 liters of airflow/day, have a 70-m(2) surface area, and undergo complete renewal every 100-400 days. Despite this, airways are susceptible to aging, injury, and diseases that are major causes of mortality. Current airway regeneration research is focused both on understanding the cells and strategies responsible for maintaining intrinsic tissue homeostasis as well as on establishing clinical interventions for improving repair.