If you’re like most people, you live in a city. More than half the world’s population now lives in cities, and that figure will go to about two-thirds of humanity by the year 2050. Cities are getting bigger. In 1990 there were ten “mega-cities” with 10 million inhabitants or more. In 2014, there were 28 mega-cities, home to 453 million people. Incredible, huh? A lot of people love cities; they’re centers of culture and business and life. The thing is, they’re also often centers of extreme poverty. To make cities sustainable for all, we can create good, affordable public housing. We can upgrade slum settlements. We can invest in public transport, create green spaces, and get a broader range of people involved in urban planning decisions. That way, we can keep the things we love about cities, and change the things we don’t.