The United for Smart Sustainable Cities initiative (U4SSC) issued a new report titled U4SSC: A guide for circular cities. The guide details the developmental and sustainability challenges that cities are facing and how the concept of a circular economy can be applied to cities. The guide details the components of the circular city framework: city assets and products (infrastructures, city resources, and city goods); circular city actions (outcome-orientated actions that can be applied to city assets and products); circular city outputs; and circular city enablers (activities which promote the implementation of circular city actions). The guide also explains the circular city implementation framework. The framework employs four steps to assist city stakeholders in setting circular actions: (a) establishing a baseline for circularity, (b) defining the potential of circularity and prioritising circular actions, (c) using city enablers to catalyse circular actions, (d) assessing these actions' impacts. The guide concludes with recommendations for implementing circular city actions and presents 17 case studies that demonstrate the application of the circularity concept in cities around the world.