Currently our world is becoming increasingly urban, with around 50% of its population living in cities. Whereas cities produce 80% of the worldwide GDP and are places with high innovation, they also consume 75% of worldwide resources and produce 80% of CO2 emissions. Thus, achieving urban sustainability will be crucial in the future. To reduce resource consumption in cities, Circular Economy has been proposed as a key concept, i.e. using resources more efficiently through value retention processes and minimizing the waste produced. Although the concept of the Circular Economy is not new, its potential contribution to Urban Sustainability still needs to be elicited. How does the Circular Economy conceptually integrate and, contribute to, Urban Sustainability? To answer this question, we focused on how the transitions towards the Circular Economy and towards Urban Sustainability are currently assessed. We conducted a cluster analysis of approximately 50 sets of indicators. Roughly half of the sets are currently used by municipalities or institutions to track the progress of cities towards the Circular Economy; the others cover Urban Sustainability. Each set contains approximately 40 indicators, although the number varies greatly. From each set, we extracted single indicators and categorized them according to conceptual frameworks, namely the three pillars of sustainability and the Sustainable Development Goals. We analyzed the overlap between the sets to derive clusters. We hypothesized that it should be possible to detect two clusters of sets of indicators: one referring to Circular Economy, one to Urban Sustainability. This would emphasize the differences in how the transitions towards Circular Economy and Urban Sustainability have been assessed, through the choice of distinct indicators. Our results will have both theoretical and practical contributions, informing the debate on the differences and overlaps between the two concepts and supporting urban communities in developing ad-hoc sets of indicators.