This meant that rather than accepting whatever happened to money supply, they would actively try to influence the amount of money available. This would influence credit creation and the overall level of economic activity. Modern monetary policy does not involve gold to a great extent. Since then, it has been the job of any country's Central Bank to control the amount of money and credit in its economy. In doing this, it wants to maintain the purchasing power of its currency and its comparative worth to other currencies.
Economists debate the relevant measures of money supply.
Economists debate the finer points of the implementation and effectiveness of monetary policy but one thing is obvious. At the extremes, monetary policy is a potent force. In countries where the printing presses run full tilt to pay for government operations, money supply is expanding rapidly and the currency becomes rapidly worthless compared to goods and services it can buy. Very high levels of inflation or hyperinflation is the result.