In real-time cities, urbanity merges with digital information so that the built environment is dynamically sensed and synchronously actuated to perform more efficiently, intelligently, and sustainably.In terms of sensing the real-time city, we can leverage existing systems that have been developed for other reasons, but which can function as sources of information about urban operation. Customized sensor networks can also be implemented to extract large amounts of information about the various processes contained within the built environment. Additionally, we can consider each urbanite a human sensor, an agent for sensing and reporting on her individual experience through user-contributed content. The crowd, therefore, becomes a distributed network of sensors that allows us to understand the dynamic patterns of the real-time city and the experiences of its citizens. In terms of actuation, we can leverage various techniques to transform the spaces of the city to responsive, context-aware environments whose inhabitants are incorporated as entities with transient preferences and needs. Instead of generic \”occupants,\” they become hyper-individualized \”users\” whose desires are taken into account by the cybernetic mechanisms that regulate the performance of the city in real time. Yet, manipulating space through embedded actuators is not the only possible means of spatially regulating urban systems: the inh abitants themselves can be considered possible agents of regulation and actuation. In this regard, once access to real-time information about how the city operates is democratized, citizens can be actuated and their actions can be self-regulated based on the real-time knowledge of urban dynamics conveyed on information-delivery platforms. Real-time Cities aims to provide the theoretical grounding and technical skills required to design, develop, and implement prototypical urban cybernetic mechanisms that sense and/or actuate the city in any of the above-mentioned categorical variations, with the promise of creating a \”smart city\” that is a desirable, safe, and sustainable place in which to live and work.