Where does adaptation to innovation take place? I present evidence on the role of agglomeration
economies in the application of new knowledge to production. All else equal, workers are more likely
to be observed in new work in locations that are initially dense in both college graduates and industry
variety. This pattern is consistent with economies of density from the geographic concentration of factors
and markets related to technological adaptation. A main contribution is to use a new measure, based on
revisions to occupation classifications, to closely characterize cross-sectional differences across U.S. cities
in adaptation to technological change. Worker-level results also provide new evidence on the skill bias of
recent innovations.