The Great Depression was a massive economic and political event that still influences the way we think about the world.
It was precipitated by the Great Wall Street Crash on 29 October, 1929. Over the next month, the value of shares on the New York Stock Exchange fell by 30%.
Banks collapsed, unemployment in the US peaked at 25% and the contagion spread through a disjointed international financial system as idiosyncratic central bankers often made things worse. Check out Liaquat Ahamed's prize-winning history 'Lords of Finance' for a cracking read of this period.
The supply of money dried up and countries put up barriers to trade as they sought to protect themselves, their industries and their populations from mass unemployment and economic chaos.
The 'New Deal' policies of President Roosevelt in the US began to partially undo the damage but it wasn't until World War II and the international institutions that were formed in its aftermath that we saw some of the economic demons safely wrangled.
So it's a big deal for the IMF to declare that the damage the world economy will sustain from Covid-19 will be "the worst economic fallout since the Great Depression."
Are they right?
Historic comparisons are problematic. There are always caveats and historical events are constantly reassessed with new research.
But when you look at the bare bones of what's very suddenly just happened, the comparisons are valid.
Stock markets have collapsed. Unemployment has surged. The value of economic output is disappearing down a very dark hole.
Paradoxically, this is perhaps where the comparisons fade and where we have to take some hope for the future.
As the IMF itself notes, the response from central banks around the globe has been to provide oceans of money to enable governments to cheaply fund their programmes of income supports and credit for businesses. The speed of this response is in marked contrast to the tentative steps taken by the ECB in particular during the Global Financial Crisis a decade ago.
The IMF praises the efforts of governments thus far to provide 'lifelines' to households and businesses but it also advises them to "do whatever it takes but make sure to keep the receipts". Because Covid-19 will have to paid for, eventually.
Of course, this is not all. There are still huge uncertainties - the obvious uncertainty is the path of the virus.
The IMF, however, says there is no trade off between managing the virus and allowing for some economic activity. It supports all the stringent public health measures under the 'Great Lockdown'.
The IMF's logic is that normal economic activity will never return while there is still a risk to human health.
This thought may sound odd coming from an institution the purpose of which is to ensure the world's economies function efficiently.
But it's a pretty strong message to send at a time when many countries are beginning to reopen parts of their economies.