More and more people are leaving rural life and moving to cities, with six out of every 10 people expected to be living in an urban area by 2030, according to the World Health Organization.
This is putting an increasing strain on how our cities provide health, education and housing for their booming populations. But there are some cities around the world that have embraced innovation to tackle their problems – be it smart transport systems, fully sustainable energy supplies or online learning.
CNBC is asking you to pick what you think is the world's most innovative city. We'll feature one city each episode, and you can keep up to date on Twitter with #innovationcities.
Here's the selection: