Inflation has come back faster, spiked more markedly, and proved to be more stubborn and persistent than major central banks initially thought possible. After initially dominating headlines in the United States, the problem has become a centerpiece of policy discussions in many other advanced economies. In 15 of the 34 countries classified as AEs by the International Monetary Fund’s World Economic Outlook, 12-month inflation through December 2021 was running above 5%. Such a sudden, shared jump in high inflation (by modern standards) has not been seen in more than 20 years.