The world economy is enjoying a synchronised recovery. But it will prove unsustainable if investment does not pick up, especially in high-income economies. Debt mountains also threaten the recovery’s sustainability, as the OECD, the Paris-based group of mostly rich nations, argues in its latest Economic Outlook. This report is the swansong of Catherine Mann, who was an outstanding OECD chief economist. It suggests that relief is legitimate, but complacency definitely is not.