Notwithstanding the voluminous studies of Hong Kong's anticorruption experience and the admiration the ICAC has earned from other governments as a model for "institutional engineering," little is known about how the public in Hong Kong has perceived and responded to corruption. Less clear is what factors beyond a powerful and independent anticorruption agency have made the Hong Kong experience possible. Drawing on original survey data collected in Hong Kong in 2010-2011, this study investigates what determines individual propensities to accept or reject corruption and explores the role of a zero-tolerance culture in preventing corruption. Evidence confirms the existence of a low tolerance for corruption in Hong Kong. It also reveals a more significant impact of informal institutions than formal ones on corruption tolerance levels. As the very first study of zero tolerance of corruption, this research adds considerable depth to our understanding of why Hong Kong has become one of the most corruption-free societies in the world and of the importance of civic engagement in deterring actual and potential corruption.