Does the turn of the twenty-first century set a new frontier in the writing of urban history? According to demographers we are advancing towards a fully urbanised world where for the first time the majority of the planet's population will live in cities, but for a European urban historian it is difficult to discern a period in contemporary history when this has not been the main trend. In fact, it has been precisely the overwhelming presence of cities in recent European history which has made it so difficult to define urban history as a distinct branch of knowledge. To some extent, the complexity of the urban fabric and the diversity of events which define an urban environment have often constrained the work of urban historians and the heuristic value of their research in comparison with the work of more established disciplines such as social and economic history, the history of planning and architecture or, even more recently, environmental history.