"Of all the troubles facing the world, the rising prevalence of dementia might seem among the less pressing. The reason behind it—longer lifespans—is to be cheered; it does not advance at the speed of a viral infection but with the ponderous inevitability of demographic change; and its full effects will not be felt until far into the future. But the reality is very different. As our special report this week makes clear, dementia is already a global emergency. Even now, more people live with it than can be looked after humanely. No cure is in the offing. And no society has devised a sustainable way to provide and pay for the care that people with it will need."