The question of how to achieve healthy, sustainable urban futures demands a singular emphasis. The scale and rate of change of modern urbanisation is unprecedented – so much so that it threatens the health gains of the past century. Urbanisation is the greatest ecological shift in human history, and in modern times has attained dimensions never seen before. We have mere decades to enact the greatest transformational change the planet has ever seen, if we are to safeguard a sustainable future. Indeed, the scope, scale, and ambition of transformative efforts need to accelerate dramatically, if humanity is to achieve sustainability before being overwhelmed by global change.