The amount of money available in an economy. In the heyday of monetarism in the early 1980s, economists pounced upon the monthly (in some countries, even weekly) money-supply numbers for clues about future inflation. Central banks aim to manage demand by controlling the supply of money through open-market operations, reserve requirements and changing the rate of interest (to be exact, the discount rate). One difficulty for policymakers lies in how to measure the relevant money supply. There are several different methods, reflecting the different liquidity of various sorts of money. Notes and coins are completely liquid; some bank deposits cannot be withdrawn until after a waiting period. M3 (M4 in the UK) is known as broad money, and consists of cash, current account deposits in banks and other financial institutions, savings deposits and time-restricted deposits. M1 is known as narrow money, and consists mainly of cash in circulation and current account deposits. M0 (in the UK) is the most liquid measure, including only cash in circulation, cash in banks’ tills and banks’ operational deposits held at the Bank of England. Although it is a poor predictor of inflation, monetary growth can be a handy leading indicator of economic activity. In many countries, there is a clear link between the growth of the real broad-money supply and that of real GDP.