Problem. Our current economic systems are deemed unsustainable. Although a global issue, the objective of living in a sustainable society is increasingly an urban challenge, as a rising 50% of the world's population currently dwell in cities. To secure a better urban future, integrated and actionable urban knowledge focused on what urban sustainability entails and how to achieve it is needed. In this context, the Circular Economy (CE) concept fosters efficient resource use through value-retention processes and waste minimization. Despite the wide attention on the CE, its interconnectedness with, and contribution to, sustainability, and whether these concepts might support or hinder each other, have not yet been clarified. Besides, knowledge is needed to guide cities towards a CE, for example, by identifying the types of interventions needed to achieve circularity, and the factors affecting the adoption of innovation that can foster it. Aim. This dissertation aims to scrutinize the CE concept applied in urban settings. It is based on a) the analysis of indicators used to assess circular cities, b) the categorization of interventions aimed at achieving a CE, and c) the identification of factors that affect the adoption of recycled products, as one measure towards CE. Approach. Indicators used to assess circularity and sustainability in urban settings were analyzed and compared. Semi-structured expert interviews were performed to iterate a framework that categorizes interventions that foster the achievement of a CE. A behavioral framework was developed that combines insights from the theory of adoption of innovation and behavioral theories, to identify and analyze the factors that can affect architects' decisions to recommend recycled concrete. A survey was used to gather quantitative insights from architects on their beliefs about the selected product. Insights. The results show that the concept of an urban CE is embedded in the broader concept of urban sustainability; however, the use of CE indicator sets entail a more detailed focus on certain thematic groups (e.g., waste production and management), for which more indicators are available in comparison with what offered by urban sustainability indicator sets. To categorize CE interventions, the proposed framework (RISE: Research & Realize, Implement, Support, Enable) offers a tool to guide the achievement of CE targets. In current circularity assessments, specifically in the construction sector, most attention is paid to implementation interventions (e.g., the quantity of material recycled). However, some of them (e.g., recycling strategies) still face barriers. Focusing on one recycling strategy (i.e., recycling concrete aggregates for recycled concrete) we inquired about the factors that affect this product's adoption. A senior position, a high level of knowledge of the material and a specific label, beliefs about the material's lower environmental impact, and prescriptive social norms affect the selected innovation's adoption. Finally, we suggest leveraging specific predictors of behavior to increase the recommendation of recycled concrete. Conclusions. This work contributed to shed light on the CE concept. This research challenged the added value of focusing on a CE rather than sustainability. Furthermore, it put forward a) an integrative perspective on achieving a CE focusing on a systemic approach, and b) a holistic behavioral framework for analyzing innovation adoption.