For over a century, starting with the work of Alfred Marshall (and also in resource economics), economic geography has emphasized the productivity of dense urban agglomerations. Yet little attention is paid to one key policy implication of economic geography’s core mechanisms: Environmental policies can aid economic development, per se—not hurting the economy to help the environment but advancing both objectives.We review mechanisms from economic geography that imply that environmental policies can deliver such win-wins: influences upon agglomeration of long-tanding natural conditions, like usable bays, which long were perceived as fixed yet now are being shifted by global environmental quality; agglomeration’s effects on other influential conditions, like urban environmental quality; and the effects of rural environmental quality on the flows to cities of people and environmental quality. Finally, we consider a geographic policy typology in asking why society leaves money on the table by failing to promote environmental policies despite the potential win-wins that we highlight.