On World Cities Day, the World Health Organization (WHO) calls on national and city leaders to transform urban areas into engines of health, equity and sustainability.

More than 4.4 billion people, over half of humanity, now live in urban areas, a figure projected to rise to nearly 70% by 2050. In cities health, inequality, environment and economy intersect in powerful and dramatic ways, creating both complex risks and unique opportunities for progress. While health challenges loom in all urban settings, the worst health outcomes are often concentrated in slums and informal settlements, with residents enduring unsafe housing, inadequate sanitation, food insecurity, and rising exposure to floods and heat. Today, 1.1 billion people live in these conditions, a number expected to triple by 2050.