Cities have a key role in climate change mitigation. Energy use associated with buildings and transportation result in significant greenhouse gas emissions, but density is a critical factor in reducing the impact of both. Given that cities have the legislative ability to regulate buildings and density, they have the potential to be very effective in mitigating the increase of carbon emissions. The effectiveness of their work is, however, contingent on the coordination of planning at a regional level that makes possible transportation options that reduces vehicular related-emissions. Two key questions arise from this. What are density patterns that are less intensive in carbon emissions? What mechanisms and approaches can facilitate, and provide incentives for, integrated approaches to density and transportation? This lecture will draw lessons and examples from leading North American cities and regions.