In an effort to spur lending the European Central Bank has introduced negative interest rates for bank deposits. Although it sounds strange, there's no reason that interest rates can't go negative -- in fact, negative interest rates are basically the same thing as traditional inflation. Spend (or lend) the money now because you'll have less in the future.
It cut its deposit rate for banks from zero to -0.1%, to encourage banks to lend to businesses rather than hold on to money.
The ECB is the first major central bank to introduce negative interest rates.
Howard Archer, chief UK and European economist at IHS Global Insight said: "Despite being widely anticipated and in some quarters criticised for occurring too late, it is still a bold and unusual move by the ECB to take its deposit rate into negative territory."
"There has to be considerable uncertainty as to how effective negative deposit rates will turn out to be," he added.
It has been tried before in smaller economies. Sweden and Denmark, who are both outside the Single Currency, attempted to use negative rates in recent years with mixed results.
Analysts said in Sweden it had little discernible impact; in Denmark it did have the effect of lowering the value of the currency, the Krone, but according to the Danish Banking Association it also hit the banks' bottom line profits.
Here's some more about what a negative interest rate even means.