How much money is circulating in the United Kingdom? The question sounds simple. In fact, it is notoriously difficult to answer, because what counts as money is not a straightforward matter. A variety of measures have been advanced, and they tell different stories about the changing supply of money in an economy. These differences are of more than merely academic interest, because measures of the money supply are inputs to the decisions of central banks. Wrong answers can lead to wrong actions, with potentially devastating economic effects. This book examines the measure of money and, in that light, the actions of the Bank of England in in the lead up to the 2008 financial crisis and its aftermath. It is essential reading for anyone interested in money, measures of its quantity, and the relationship between the money supply and the economic cycle.