During development, the lung endoderm is patterned along its anterior-posterior axis, giving rise to distinct epithelial lineages, such as the alveolar cells that mediate gas exchange, and the basal and secretory cells that line the airways. In this issue (p. 108), Edward Morrisey and colleagues show that the polycomb repressive complex 2 component Ezh2 restricts the basal cell lineage during lung development, thereby allowing correct patterning of the lung. The researchers report that Ezh2 is broadly expressed in the lung during early development but then gradually becomes downregulated as development progresses. Importantly, they demonstrate that the endoderm-specific deletion of Ezh2 impairs secretory cell differentiation while inducing the ectopic and premature development of basal cells that express the transcription factor Trp63 and other basal cell markers. Furthermore, they report that Ezh2 deletion gives rise to a cell population that might represent an intermediate state between basal and secretory states. These and other findings indicate that Ezh2 controls the phenotypic switch between basal cells and secretory cells, and regulates both the temporal and spatial patterning of the lung.