In the form it is known today, macroeconomics began in 1936 with the publication of John Maynard Keynes’s “The General Theory of Employment, Interest and Money”. Its subsequent history can be divided into three eras. The era of policy which was guided by Keynes’s ideas began in the 1940s. By the 1970s it had encountered problems that it could not solve and so, in the 1980s, the monetarist era, most commonly associated with the work of Milton Friedman, began.