English-language analysis of Chinese foreign policy has often cited nationalist public opinion as a key driver of Beijing’s recent assertive maritime conduct. Yet these important conjectures have not been systematically tested. How can we know whether public opinion has been driving an authoritarian state’s foreign policy? What are some cases in which concern about popular nationalism may have influenced Beijing’s behavior in disputed maritime spaces? To answer these questions, this article constructs a methodological framework for assessing the likely impact of public opinion on particular instances of state action. Applying this to five cases typical of China’s on-water policy in the South and East China Seas since 2007 indicates that popular nationalism has had little to do with China’s assertive turn on its maritime periphery.