Book excerpt: Why has there been uneven success in reducing air pollution even in the same locality over time? This book offers an innovative theorization of how local political incentives can affect bureaucratic regulation. Using empirical evidence, it examines and compares the control of different air pollutants in China-an autocracy-and, to a lesser extent, Mexico-a democracy. Making use of new data, approaches, and techniques across political science, environmental sciences, and engineering, Shen reveals that local leaders and politicians are incentivized to cater to the policy preferences of their superiors or constituents, respectively, giving rise to varying levels of regulatory stringency during the leaders' tenures. Shen demonstrates that when ambiguity dilutes regulatory effectiveness, having the right incentives and enhanced monitoring is insufficient for successful policy implementation. Vividly explaining key phenomena through anecdotes and personal interviews, this book identifies new causes of air pollution and proposes timely solutions. This title is also available as Open Access on Cambridge Core.