The planet is now dominated by cities. And it is becoming very clear that the future of humanity--global sustainability itself--is now dependent on us having an understanding, a deep understanding, of cities and urbanization. You now have the greatest migration in history where billions of people are choosing to come to cities; to change their lives radically from what it traditionally was. Look, historically, the hallmark of any civilization is cities. In fact, some anthropologists and archeologists have even said that cities (and I agree with them) cities are actually one of our main inventions. The fact that China and India are building hundreds of new cities, and this is going to have an enormous impact. They are sort of the fastest, most spectacular social phenomenon that ever happened to our species and, perhaps, to biology on Earth. There's lots of research done on cities. There's lots of economists who study cities and sociologists and anthropologists, and even psychologists; and the work that we are involved in is bringing a predictive mathemetizable framework to that, to complement the traditional narrative form more associated with the social sciences, and trying to understand what is systematic of cities, so we can predict behavior, and have an impact on problem- solving. I think Jane Jacobs once said that one of the hardest problems about understanding cities is that they deal with dozens of quantities; they all intertwine. So a city is not just its economy, it's not factoring it's just producing something from inputs, it's not just a set of people interacting with each other without structure or context or economics; and it's not just an infrastucture, either. And cities, we recognize now, are the origin of what we perceive to be problems. Global climate warming, our environment, problems with the economy, problems with disease, with pollution. However, cities are also the origin of the solution. They are the places where ideas are created, they are vacuum cleaners that suck up creativity and Innovation. People are attracted to cities by the buzz of cities. So, we need to understand how these two things integrate. If I can give you the recipe to have a wealthy, innovative city, why is it so hard to recreate that recipe? What is really going on in San Jose? I can tell you San Jose is very inventive; it's very creative; but what is it about that place? One of the metaphors that has been used consistently for cities is to compare them to organisms. One often hears phrases like "the metabolism of the city," or "the DNA or the marketplace," or even the ecology of the urban system. So, one of the questions, obviously, that arises, is "is that just metaphor, or is there something serious and substantive in it?" So scaling is to look at how the properties of a system vary with its size. In Biology, we see that the bigger you are the less you need per capita; the less energy you need per capita, et cetera. So there is an economy of scale. Associated with that is the slowing of the pace of life. You live longer, things diffuse slower, hearts beat slower, etc. In cities, we see the opposite behavior. As cities get larger, what you see is a systematic increase in socio-economic products. So you find that wealth creation gets faster, innovation gets faster. So all of the things associated with social interaction increase in the same way, and that increase can be expressed very simply, and that is: If you double the size of a city, you get approximately a 15% increase in wages, wealth, innovation, and also the negative effects of living in a city... So in this sense you can see what a city is. The city is a concentration of people, with the infrastructure that allows you to basically concentrate interactions effectively--in terms of number of interactions per unit time--shrink time and shrink space, so that you create, essentially, a social accelerator, a social concentrator of human activity. So in Biology a network is, your cardiovascular system, your respiratory system, your renal system; whereas, in cities, it's the roads, the electrical lines, the gas lines, but it is also the social networks of interaction between people, and between groups of people. We believe that the reason we see these extraordinarily systematic behaviors in both biology and in social organizationsms - cities - is because of the constraints of networks. But there are specific ways in which cities can deviate from these averages, as well; in terms, for example, of how well they do economically. These have a lot to do with their history and some of the self- reinforcing cycles... The various historical events that took place; the multiple commissions of urban designers and architects; the role of the various mayors; the fact that the railroad may have suddenly come through. So I think now that we have an increasingly clear picture about what cities look like quantitatively - in terms of their statistics in terms of how much they can vary from this idealized generic city - I think what's missing now is to have a mathematical description that's predictive of what creates these patterns that we see in the data. The science of cities means that, in addition to just qualitative understanding of a city, that the structure, dynamics, organization, evolution, growth, can all be put in a mathematizable way, quantitatively, and therefore predictively. So the only way to understand all this together is to understand how these different aspects of the city condition each other and constrain each other to create sort of this magical dynamics in organization that is organization. I would say that if you care about the history of humanity, if you care about economic growth, if you care about innovation, you have to think about cities.