Cities are getting more complex as their residents acquire more and more ways in which they can interact with one another. New technologies enable individuals to repackage their time and space in countless different combinations, and the flexibility afforded by such innovations makes possible many new ways in which individuals might react to this complexity. Behavioural change is considerably greater in the modern city than the medieval. Delivered by Professor Mike Batty: Director, Centre for Advanced Spatial Analysis, University College London.