2007 is the year that the world's population becomes more urban than rural for the first time. This exciting series explores some of these global cities, and looks at how the challenges of urbanisation, globalisation, citizenship and sustainability are being met and answered.

Violent drug gangs rule the vast slums, or favelas, that are home to nearly a fifth of Rio de Janeiro's population. Away from the slums, the city's beaches, Carnival, and scenery attract tourists from around the world. Foreign businesses are drawn here because of abundant energy supplies.