Hundreds of cities, counties, and even states made (or renewed) a public commitment to reducing greenhouse gas emissions. Some local governments made this commitment in response to President Trump’s decision to withdraw from the Paris Climate Agreement. Others re-affirmed an existing commitment. For more than a decade, cities – both large and small – have recognized the economic advantages associated with sustainability, and have set aggressive goals. At the same time, sustainability advocates have long argued that cities – with zoning authority and direct accountability to a local population – are best poised to lead on sustainability. From recycling policies, to planning decisions that make it easier to bike to work, cities are where change is happening.