Research frame:The concept of a smart city is closely related to sustainability. The circular economy is one of the most interesting facets of the latter. Nevertheless, no substantial effort has been made so far to establish the link between the circular economy and smart cities.Purpose of the paper: Through the conceptual systemic perspective and quantitative means, the study investigates how the concepts of the smart sustainable city and the circular economy are interconnected.Methodology: After assessing the related scholarly literature to highlight the systemic nature of the connection between a smart sustainable city and a circular economy, we analyze the relationship between the two by operationally quantifying both concepts on the macro level and the level of the single components of smartness and circularity. Operationalizations are based on the relative frequencies with which certain EU cities are mentioned in scholarly documents related to smartness and the circular economy and indexed on Google Scholar. Regression analysis and principal component analysis are used as the main analytical tools.Findings: We find a significant positive relationship between a city's smartness and circularity. While the presence of specific smart city-related technologies like AI, Big Data, and IoT are less important for the proliferation of circular economy initiatives in a city, the same is not true for the overall presence of an advanced ICT infrastructure. Alternatively, waste management is the element of the circular economy that contributes the most to sustainable urban smartness.Research limits: The analysis is performed on a dataset consisting of 193 EU cities. Therefore, the results cannot be applied to cities outside the EU. Moreover, the indices that operationalize sustainable smartness and circularity are empirically valid but require more in-depth statistical validation.Practical implications: The study suggests city managers and administrators to treat the smart sustainable city concept holistically. Indeed, circular economy initiatives could significantly affect the implementation of smart sustainable urban initiatives.Originality of the paper: Although the literature treats the two concepts extensively, no attempts to quantify the relationship between smart sustainable cities and circular economy have been made until now. We hope this study will shed additional light on the complex systemic nature of the investigated domains.