Chapter 7: The Mundell-Fleming Model
7.1 Introduction
We now turn to develop a complete model of an open macro economy. This model will
allow us to consider how a variety of possible events might influence output levels, interest rates,
the current account balance, and the exchange rate. The model we develop is the open economy IS-
LM model, otherwise known as the Mundell-Fleming model. This model was first developed in
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the early 1960s, and it remains the workhorse open economy macro model to this day. It is a
remarkably useful model for understanding how economic policies as well as various types of
economic shocks might influence an economy and how openness to the international economy
impacts events at home.
The Mundell-Fleming model extends the standard IS-LM model by adding, wherever
appropriate, international components that affect equilibrium conditions in the goods and assets
markets. It also includes an additional curve that, depending upon the exchange rate regime in place
for the country, identifies the equilibrium condition for a stationary value for the exchange rate or
for a zero balance in the overall balance of payments.
This curve is called the BB curve. Solving
the overall model will involve deriving the behavior of each of the three curves and finding a point
of common intersection that will determine the equilibrium values for each of the endogenous
variables in the model. In what follows we will build an algebraic model as well as a graphical
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The model was first developed by Robert Mundell, now at Columbia University, and the late J. Marcus
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Fleming, while both were staff economists at the International Monetary Fund.
In 1999, Mundell won the Nobel
Prize in Economics for his work on this model.
A fourth macro-economy market, the labor market, can easily be added to this setup. That market would
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determine the overall level of full employment, and allow for a discussion of how the price level might change in
response to tightness in the output or (equivalently) the labor market. For the time being we will assume that prices
are fixed and ignore this market.

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