Although the fields of urban planning and public health share a common origin in the efforts of reformers to tame the ravages of early industrialization in the 19th century, the 2 disciplines parted ways in the early 20th century as planners increasingly focused on the built environment while public health professionals narrowed in on biomedical causes of disease and disability. Among the unfortunate results of this divergence was a tendency to discount the public health implications of planning decisions. Given increasingly complex urban environments and grave health disparities in cities worldwide, urban planners and public health professionals have once again become convinced of the need for inclusive approaches to improve population health and achieve health equity. To make substantive progress, intersectoral collaboration utilizing ecological and systems science perspectives will be crucial as the solutions lie well beyond the control of any single authority. Grounded in the social determinants of health, and with a renewed sense of interconnectedness, dedicated and talented people in government agencies and communities who recognize that our future depends on cultivating local change and evaluating the results can come to grips with the enormous challenge that lies ahead to create more equitable, sustainable, and healthier cities worldwide.