Indeed, though perhaps not on a par with global warming and looming water shortages, obesity – and especially childhood obesity – nonetheless is on the short list of major public-health challenges facing advanced countries in the twenty-first century, and it is rapidly affecting many emerging-market economies as well. Yet solving it poses much more difficult challenges than the kind of successful public-health interventions of the last century, including near-universal vaccination, fluoridation of drinking water, and motor-vehicle safety rules.