In macroeconomic models, the nominal money supply, the long-term nominal interest rate, or even the inflation rate usually serves as the monetary policy variable. In practice, however, none of these variables is directly controlled by the central bank. Consequently, these models do not accurately reflect the implementation of monetary policy. Based on a theoretical model which incorporates the main institutional features of the euro area, this paper analyzes the transmission of monetary policy impulses from their implementation (setting the interest rate at which banks can obtain liquidity from the central bank) via the interbank market to the aggregate money and credit supply in an economy. Building on this analysis, we discuss the ability of the central bank to steer its operating target, the interbank market interest rate, and the money supply.