Since the observed growth rates of the monetary aggregates, M1B and M2, often diverge, monetary policymakers, their advisors, and “Fed watchers” naturally question which aggregate is a better measure on which to focus in conducting monetary policy. This article provides some direction to this perennial debate: The evidence indicates that the growth of M1B is influenced relatively less by nonpolicy activity—that is, it is easier to control—than M2 and that the growth of M1B better explains variations in the pace of economic activity than M2.