Jane Jacobs’s 1961 classic, The Death and Life of Great American Cities, identifies four preconditions for the creation and preservation of vibrant, diverse cities: (1) high densities of population and activities; (2) mixtures of primary uses; (3) small-scale, pedestrian-friendly blocks and streets; and (4) retaining old buildings mixed in with new. These principles are directly at odds with the underlying presumptions of Euclidean zoning. Euclidean zoning and related subdivision regulations restrain density, separate primary uses, favor roadway designs based solely on traffic needs, and ignore the preservation of older buildings. Since 1961, we have erected a ramshackle superstructure of project-specific review procedures, while leaving untouched the underlying presumptions of Euclidean zoning. A rethinking of Euclidean zoning, consistent with Jacobs’s principles, requires regulatory strategies that work at different scales. At the scale of the street, zoning should focus on how private buildings help create and activate the public space of the street. At the scale of the urban district, codes should offer strong incentives for mixtures of primary uses and reuse of older buildings. At the scale of the metropolitan region, state oversight of local and regional planning should favor the coordination of denser, compact developments with public investments in transit.