Using single-cell RNA sequencing, a Yale University-led team has built an atlas of aberrant cellular populations in idiopathic pulmonary fibrosis (IPF), a fatal interstitial lung disease characterized by irreversible scarring of the distal lung. As they report in Science Advances, the investigators profiled 312,928 cells from 32 IPF patient lungs, the lungs of 28 smoker and nonsmoker controls, and 18 lungs from individuals with chronic obstructive pulmonary disease.