The Constitution states explicitly: "To coin Money, regulate the Value thereof..."
Here's a good explanation:
"The Federal Reserve Bank hires the US Treasury to print up some money. The Federal Reserve only actually pays the treasury for the cost of the printing, they do NOT pay $1 for each 1$ printed. But the Federal Reserve turns around and loans out that money (or credit line) to banks at full face value, those banks which have exhausted their deposits then loan that Federal Reserve fiat money to you, and you must repay it in the full dollar value (plus interest) in work product, even though the Federal Reserve printed that money for pennies, or created it out of thin air in a computer.
As the Federal Reserve overprints more money, the money supply inflates, and too much money starts chasing too few goods and services, which means prices go up. But contrary to the charade put on by the Federal Reserve, inflation doesn't just come and go due to some arcane sorcery. The Federal Reserve can halt inflation any time it wants to by simply shutting down those printing presses. It therefore follows that both inflation and recession are fully under the control of the Federal Reserve. This means the cycle of inflation and recession is an intentional one; a gigantic heartbeat that pumps paper certificates out to the working class, while pumping real wealth in to the owners of the banks.
So here we are with a bank that legally counterfeits the money you borrow but expects a full value (plus interest) repayment."
It is not true to its origin or purpose in practice AT ALL!
"If the American people ever allow PRIVATE banks to control the issue of their currency, first by inflation, then by deflation, the banks will deprive The People of all property until their children wake-up HOMELESS on the continent their fathers conquered. The issuing power should be taken from the banks and restored to The People, to whom it properly belongs". --- Thomas Jefferson