Cities are severely affected by the air pollution and climate change caused by the transportation sector. From bans on diesel cars to low- and zero-emission zones to soot-free electric buses, cities have reacted with policies intended to drive the transition to a decarbonized transport sector, and have collectively emerged as major players in this policy area. In recent years, the ICCT has worked closely with city governments on remote sensing through initiatives such as the Real Urban Emissions Initiative (TRUE), on zero-emission buses, and on policies for local electric vehicle market development and charging infrastructure needs modeling. These three workstreams form the core of our city-based strategy: highlighting elevated emissions from the existing combustion fleet, helping cities procure clean buses, and creating a race to the top for policies to drive the transition to electric vehicles. A central element of our strategy is for cities to play a critical role in accelerating policymaking to achieve the pace of needed transportation-related emissions reductions that both deliver direct and local benefits and substantially increase the level of ambition for provincial, national, and international level policies.