Urbanization and the concentration of population and activity traditionally have brought cities an array of environmental quality and pollution issues. The process through which cities have responded to their air pollution problems are equally varied. This application chapter focuses on the narratives of three cities and an urbanized region: London, UK; Los Angeles, US; Rhine-Ruhr River Valley, Germany; and Tokyo, Japan. In all cases, worsening air pollution began to have clear and often immediate economic consequences and human health impacts. While different, several important similarities were present among the crisis-to-transformation processes for each city. These include an extended history of ever-worsening air quality conditions, often punctuated or accelerated through large-scale social or environmental trauma, the emergence and rapid application of new science and technology, and the concomitant innovation in public policy and governance capacity to address the problem of urban air pollution. The desire to address urban air pollution became both an economic imperative and an ambition to protect the well-being of the cities’ residents and to restore the sentiment that the communities were pleasant and healthy places in which to live.