Human health and prosperity, the built environment and sustainability are interdependent. Cities are the most obvious manifestation of the built environment and should be the focus of our attention. They play such an important role in our health and well-being that we must keep working to get them right by creating a continuum of city sustainability improvement. At the same time, they are bad for our health and the health of our planet. In this chapter, we consider the role they play, some of the consequences of their early development, the links to human health and climate change and why we all need to pay more attention to our buildings and infrastructure. There is some positive news from Asia and Africa in terms of action that has been taken.