Towns and cities in the world’s developing countries are growing on an unprecedented scale. Ten years ago, an estimated 40 percent of the developing world’s population – or 2 billion people – lived in urban areas. Since then, their numbers have expanded almost twice as fast as total population growth, to more than 2.5 billion. That is the equivalent to almost five new cities the size of Beijing, every 12 months. By 2025, more than half the developing world’s population – 3.5 billion people – will be urban. While urbanization in Europe and North America took centuries, spurred on by industrialization and steady increases in per capita income, in the developing world it will occur in the space of two or three generations. In many developing countries, urban growth is being driven not by economic opportunity but by high birth rates and a mass influx of rural people seeking to escape hunger, poverty and insecurity.