In this chapter, we define smart cities across two perspectives: first with respect to the way new technologies are being physically embedded into the city, and second with respect to the way these technologies are being used to develop new forms of behaviour in terms of the way we interact with one another based on email, social media, web access and so on. These perspectives coincide and mutually reinforce one another but they do define different views of what the smart city actually is and where its focus should be. A related distinction is with respect to urban dynamics between what we call the ‘high frequency’ and the ‘low frequency city’, the former being structured in terms of routine, short term changes in location and interaction over seconds, minutes, hours and days in contrast to much longer term change over years and decades, even centuries that constitute the low frequency city. When we concatenate all these distinctions, this poses a wide array of possible views of the city, all of which compete for pride of place in the smart city movement. We argue that to plan such complexity, we need to replenish and extend our existing theories of how cities evolve and change and to this end, we need to fuse ideas about big data that are a consequence of the high frequency city with our existing models and methods that involve spatial analysis and urban simulation. We conclude with some cautionary remarks about the role of big data and the quest for a new theory of the smart city.