This paper explores when and how considerations of population health have influenced the creation, planning and management of cities. Cities – now the dominant human habitat – must be planned and managed sustainably in a world that is manifestly experiencing increasing environmental and social strains. Early industrialisation entailed crowding, squalor and industrial environmental blight; the two great associated public health hazards were infectious diseases and air pollution. These hazards have been largely controlled in rich countries. Today’s main urban health hazards are obesity (with its life-shortening health consequences) and the huge contribution of cities to climate change with the resultant risks to population health. These and other health issues in urban environments need to be understood and addressed at the community or population level. This is an ecological challenge, crucial to attaining real sustainability.