The St. Louis model of the early 1970s, as described by Andersen and Carlson (1972), was a small-scale monetarist model of economic activity. Its structure was sharply at variance with the framework of the major, larger scale macroeconometric models used for policy analysis by the Federal Reserve, both at the time of the inception of the St. Louis model and today. The St. Louis model had four major features: (i) It was sufficiently small that one could actually understand how it worked by looking at the model’s behavioral equations and by conducting simulations of it. (ii) It could be used for policy analysis, specifically for studying the effects of monetary and fiscal policy on inflation, output, and interest rates. (iii) The monetarist background of its authors meant that the model (1) focused on the quantity of money as the key measure of the stance of monetary policy and (2) contained structural linkages from money to economic activity that are now widely accepted, including the central role of a long-run demand for money that is a relatively stable function of a small number of variables. (iv) It combined short-run non-neutrality of changes in money with long-run neutrality, in line with the perspective of Friedman and Schwartz (1963a and b).