The interest rate is a monetary mechanism that serves to keep inflation under control. Inflation is a monetary phenomenon, caused by excess currency in circulation. Thus, the more money in circulation, the higher the interest rate tends to be. Conversely, when the money supply is smaller, inflation will be lower. Consequently, the interest rate will be low. Similarly, when the money supply is high, spending on the economy increases (and causes inflation). When the money supply is low, less money will be in circulation and spending will decrease. Inflation will be low. And the interest rate too!
