Having a high demand for materials and vast emissions, cities are ideal laboratories for exploring the circular economy. The circular city as a city label has attracted a lot of attention from academics and practitioners. However, it remains unclear what a circular city is in the context of the circular economy in the urban environment. To improve our understanding of how circular cities have been defined and developed by scholars, this book chapter reviews academic literature. First, we set a search scope of relevant literature using a bibliometric approach to build a database with 109 peer-reviewed articles. Then, we compile a final list of 28 definitions which are analyzed to find the dimensions of a circular city. These circular city dimensions are: system structure, components, principles, goals, and organizational characteristics. In sum, this chapter provides a comprehensive understanding of the current central themes of circular cities and their shortcomings.