Since the early 1980's, a major focus in researching for the economic variables such as interest rate, income, exchange rates and inflation rates gained importance in the literature of demand for money. The present book estimates a stable long-run equilibrium relationship between money demand and its explanatory variables in South Africa over the period of 1990 to 2007 using cointegration and error correction methods. The results indicate that monetary policy is effective but for its efficiency it does not have a quick effect; it needs at least three quarters (nine months) from the day it is made in order to make a difference. In other words, there are difficulties of implementing monetary policy in emergence situation. Therefore, monetary authorities in South Africa should take in consideration that their policy decisions need three quarters to achieve their aim. Hence, monetary policies have to be ahead. Thus, interest rates have to be set based on what inflation might be over the coming three quarters.