Policy makers around the world are turning to smart city projects in an effort to address the challenges of population growth, energy efficiency, and environmental sustainability. Previous studies have evaluated the effect of smart city projects on air quality. However, evidence on the impact of the projects on energy efficiency remains unclear. This study gathered prefecture-level city panel data in China, and used three strategies, namely a difference-in-differences estimator, a matching difference-in-differences estimator, and a counterfactu...