The preeminent argument of 20th-century economics, regarding the political utility of marco- and microeconomics, took shape in the interwar rivalry between John Maynard Keynes and Friedrich Hayek. Keynes, a Cambridge don and Bloomsbury intimate, was a ‘public intellectual’ wile Hayek, an Austrian emigre who found a home at the London School of Economics, was a theorist who only later turned to polemics. Keynes held the economy could be managed, primarily on the demand side, and rejected conventional belief in the necessity for equilibrium between savings and investment. The 1936 publication his General Theory of Employment, Interest and Money transformed Western economic and political consensus, predominating through ~ 1980. Surprisingly, his rival made no reply, in contrast to his dogged challenges to Keynes’ earlier works. Hayek, defending the laissez-faire view of Alfred Marshall and Ludwig von Mises, contended that to manage demand is to manage prices, which is the individual’s role, and thus to court either inflation or contraction; further, when the stimulus is removed, increased consumption will collapse. The amount of money and speed of its movement is key to understanding an economic system. Yet improved ability to measure and calculate did not substitute for qualitative understanding: individual decisions can never be anticipated or planned. (In this respect, he agreed with Keynes that the economy rarely comes to rest, the classical equilibrium.) Keynes, later accused of being a socialist fellow traveler — not unfairly due to his Fabian associates — shrugged off planning as the route to totalitarianism, contending tyranny results from collective sociopolitical choice. Keynes began to recover ground with the 1949 founding of the libertarian Mount Pelerin society and his decamping for America. More important, at the University of Chicago, economists led by Milton Friedman, though accepting the macroeconomic premise of laissez-faire as an inadequate policy, embraced prices as core to understanding. Subsequent ‘freshwater’ economists determined inflation to be the main objective of public policy (unlike the ‘saltwater’ view of unemployment as paramount) and gave rise to supply-side economics embraced by Margaret Thatcher and Ronald Reagan. Moving faster than in the years of the Keynes-Hayek rivalry, the author sketches the decline of Keynesian economics over 1970-2000s. Ultimately, however, Wapshott’s history of ideas is a polemic in its own right: the Bush administration’s response to the Global Financial Crisis is portrayed as necessarily Keynesian, rather than the preliminary moves of an outgoing administration, and the last word is given by the Keynesian John Kenneth Galbraith against the now straw-man Hayek, without reference to the supply siders.