This lecture explores the deep interconnection between cities and the environment. It shows how cities impact on the local and global environment through the vast consumption of energy and production of pollution; how cities are deeply impacted by changing environmental conditions; and how cities can address the environmental impacts produced within their boundaries. The lecture concludes by demonstrating that many of the world’s most significant environmental issues are in fact issues of urbanization as well. Cities are the sites of some of the most damaging environmental impacts. They also hold the promise of producing solutions to environmental challenges at a global scale. Matti Siemiatycki is Canada Research Chair in Infrastructure Planning and Finance, and the Interim Director of the School of Cities at the University of Toronto. His research and teaching focus on infrastructure planning, finance, and project delivery.