The rationale of this book follows dilemma (see introduction, this volume): The last four decades have witnessed the emergence of CTC (complexity theories of cities) —a domain of research that applies complexity theories to the study of cities. Studies in this domain have demonstrated that, similarly to material and organic complex systems, cities exhibit the properties of natural complex systems and, that many of the mathematical models developed to study natural complex systems also apply to cities. But there is a dilemma here as cities are large-scale artifacts and artifacts are essentially simple systems. So what makes the city a complex system? To answer this question I first draw attention to the ways in which cities differ from natural complex systems and suggest that, as a result, we have to include the cognitive capabilities of urban agents in theorizing and simulating the dynamics of cities. In particular, I draw attention to the fact that urban agents are typified by chronesthesia, that is, the ability to mentally travel in time, back to the past and forward to the future. From the recognition of this cognitive capability follows, firstly, a novel view on the dynamics of cities and the role of urban planners and designers in their dynamics. Secondly, a potential for a new field of study in which planning and design are not treated as external interventions in an otherwise spontaneous and complex urban process, but rather as integral elements in its dynamics.