Over the last 100 years, the world’s urban population has grown more than tenfold, and now close to half the world’s population lives in urban areas. Many aspects of urban change are unprecedented, including not only the size of the world’s urban population but also the number of countries becoming more urbanized and the size and number of very large cities. Many urban changes are dramatic – there are dozens of cities whose populations grew twentyfold in the last 50 years. Rapid urban change has often brought serious environmental problems; there are also serious (and growing) problems of urban poverty.

But there are many positive elements to these urban changes. Within lower-income nations, rapid increases in the proportion of people living in urban areas are usually a result of stronger, more diverse economies. The increase in the proportion of people living in urban centers worldwide over the last 100 years has been fuelled by the expansion of the world’s economy, most of which took place in industrial and service enterprises located in urban areas. Since most economic growth continues to be in urban-based enterprises, the trend towards increasingly urban populations is likely to continue.