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Should a government facing a recession devalue its currency, or does that merely ignite inflation? Can a central bank insulate domestic employment from foreign interest-rate shocks, or are capital flows too powerful to resist? These questions define open economy macroeconomics, the branch of the discipline that studies how international trade and capital mobility alter the effects of fiscal and monetary policy. The subfield emerged in the 1960s as the Bretton Woods system of fixed exchange rates began to strain, and it has since passed through four major frameworks, each one a response to the empirical and theoretical limits of its predecessor.
The first systematic framework for open-economy policy analysis was built by Robert Mundell and Marcus Fleming in the early 1960s. Their model—now called the Mundell-Fleming model—extended the closed-economy IS-LM apparatus to include a balance-of-payments (BP) curve. The BP curve represented combinations of income and the interest rate at which the current account and capital account together were in equilibrium. By adding this third curve, Mundell and Fleming could ask a question that closed-economy Keynesianism could not: does the exchange-rate regime determine which policy instrument works?
Their answer became a staple of policy advice. Under fixed exchange rates, fiscal policy is powerful because an expansion shifts the IS curve, raises income, and the central bank must accommodate the resulting money-demand increase to defend the peg. Monetary policy, by contrast, is powerless because any attempt to lower the interest rate triggers capital outflows that force the central bank to reverse the money-supply change. Under floating rates, the roles flip: fiscal policy is weakened by exchange-rate appreciation that crowds out net exports, while monetary policy gains strength because a lower interest rate depreciates the currency and boosts exports. This assignment of instruments to targets—fiscal policy for internal balance, monetary policy for external balance under fixed rates, and the reverse under floating rates—dominated macroeconomic policymaking through the 1960s.
The framework was Keynesian in its assumption that prices were sticky and output was demand-determined in the short run. It treated the exchange rate as a policy tool and the balance of payments as a constraint that could be managed through interest-rate adjustments. Yet the model had a serious blind spot: it said almost nothing about the money supply or the price level. The BP curve was drawn for a given domestic price level, and the current account depended only on income and the exchange rate, not on relative prices. This omission would become the target of the next framework.
By the early 1970s, the Bretton Woods system had collapsed, and many countries experienced simultaneous high inflation and balance-of-payments deficits—a combination the Mundell-Fleming model struggled to explain. The Monetarist Open Economy Macroeconomics framework, often called the Monetary Approach to the Balance of Payments (MABP), offered a different starting point. Instead of treating the balance of payments as a flow of goods and capital that could be managed with interest-rate policy, the MABP saw it as a monetary phenomenon: a sustained payments deficit was simply the result of an excess supply of domestic money.
The logic was straightforward. In a small open economy with fixed exchange rates, the domestic price level is tied to the world price level through purchasing power parity. The demand for money is a stable function of real income and the interest rate. If the central bank creates more money than people want to hold, the excess flows abroad through a payments deficit, and the money supply automatically contracts until equilibrium is restored. Under floating rates, the same mechanism works through the exchange rate: an excess money supply depreciates the currency, raising the domestic price level and restoring real money balances. The key policy implication was that sterilized intervention—buying or selling foreign exchange to offset a payments imbalance—could not permanently affect the money supply or the balance of payments. Only monetary policy mattered for the external accounts.
This framework directly challenged the Mundell-Fleming model's assumption that the BP curve could be shifted by interest-rate changes alone. The MABP insisted that any policy affecting the money supply would eventually feed through to prices and the exchange rate, neutralizing real effects in the long run. It preserved the monetarist commitment to long-run neutrality of money and extended it to the open economy. But the MABP assumed continuous purchasing power parity and full employment, which made it hard to explain the persistent real exchange-rate misalignments and unemployment of the 1970s and 1980s. The next framework would keep the monetarist emphasis on expectations but drop the assumption that prices adjust instantly.
The New Classical Open Economy Macroeconomics of the 1980s applied rational expectations to open-economy settings, with radical implications for policy. If private agents understand the policy regime and form expectations consistent with the model, then anticipated monetary policy cannot affect real output or the real exchange rate—only unanticipated shocks can. This was the open-economy version of the Lucas critique and the policy-ineffectiveness proposition.
A central result came from the work of Jacob Frenkel and others on exchange-rate determination. In a world of rational expectations and continuous market clearing, the exchange rate should follow a random walk: all available information is already incorporated into the current rate, so only news moves it. This implied that sterilized foreign-exchange intervention was completely ineffective, because rational agents would see through any attempt to manipulate the exchange rate without changing monetary fundamentals. The framework also argued that the current account was largely irrelevant for policy, since intertemporal optimization by forward-looking agents would produce whatever current-account path was consistent with consumption smoothing.
Compared to the monetarist framework, the New Classical approach was more extreme in its rejection of activist policy. The MABP had said that monetary policy mattered for the balance of payments and the price level, even if it was neutral in the long run. The New Classical framework said that even short-run real effects were impossible unless the central bank could systematically surprise the public. This conclusion rested on the assumption of continuous market clearing—prices and wages adjust instantly to all shocks. By the late 1980s, the empirical evidence had turned against this assumption. Exchange rates were far more volatile than fundamentals could explain, and disinflations in countries like the United States and the United Kingdom produced sustained output losses, not the costless disinflation that rational-expectations models had predicted. The subfield needed a framework that could keep microfoundations and rational expectations while restoring a role for sticky prices and demand-side policy.
The New Open Economy Macroeconomics (NOEM), launched by Maurice Obstfeld and Kenneth Rogoff in their 1995 paper "Exchange Rate Dynamics Redux," provided that synthesis. The Redux model built a dynamic general-equilibrium framework with optimizing households and firms, monopolistic competition, and sticky prices set in the currency of the producer. It was the first open-economy model that combined the microfoundations and rational expectations of the New Classical approach with the sticky prices and demand-determined output of the Keynesian tradition.
The Redux model produced several results that reshaped the field. First, it showed that a monetary expansion could raise domestic output and welfare even under rational expectations, because sticky prices prevented immediate adjustment. Second, it provided a rigorous welfare metric for evaluating international policy coordination: a coordinated monetary expansion could benefit both countries by internalizing the terms-of-trade externality that each country's central bank would otherwise ignore. Third, it revived the Mundell-Fleming insight that the exchange-rate regime matters for the transmission of shocks, but now grounded that insight in intertemporal optimization and explicit welfare analysis.
NOEM did not simply revive Keynesian open-economy macroeconomics; it transformed it. The Mundell-Fleming model had treated the current account as a flow determined by income and the exchange rate. NOEM treated it as the outcome of intertemporal saving and investment decisions by forward-looking agents. The older model had no explicit welfare criterion; NOEM made welfare analysis central, allowing researchers to compare the costs and benefits of alternative exchange-rate regimes, capital-account liberalization, and policy coordination. The framework also absorbed the monetarist insight that monetary policy is the primary determinant of the long-run price level, but it showed that monetary non-neutrality could persist for years because of sticky prices and imperfect competition.
Today, NOEM remains the dominant framework, but it has evolved in several directions. One active debate concerns exchange-rate pass-through: if firms set prices in the consumer's currency rather than the producer's currency, the expenditure-switching channel of monetary policy is weakened, and the welfare gains from coordination may be smaller. Another debate involves financial frictions: the 2008 global financial crisis showed that gross capital flows, banking-sector balance sheets, and sudden stops matter for macroeconomic stability in ways that the standard NOEM model, which assumes frictionless financial markets, does not capture. A third debate concerns policy coordination: while NOEM provides a framework for evaluating coordination, the empirical magnitude of the gains remains contested, and many central banks continue to act independently.
Despite their differences, the frameworks that remain active today—primarily NOEM and its extensions—agree on several points. They agree that monetary policy has real effects in the short run because prices are sticky, and that those effects are transmitted internationally through exchange rates and trade flows. They agree that expectations matter for exchange-rate dynamics and that policy credibility can reduce the output cost of disinflation. They agree that the current account reflects intertemporal choices, not just trade flows, and that sustained deficits are not necessarily a sign of policy failure.
They disagree, however, on the size and persistence of real effects. Some NOEM models with high pass-through imply that monetary policy has large expenditure-switching effects; others with low pass-through imply that the exchange-rate channel is weak. They disagree on whether financial frictions are a second-order complication or a first-order feature that requires rebuilding the model from the ground up. And they disagree on whether international policy coordination yields large welfare gains or whether the gains are small enough that independent policymaking is nearly as good. These disagreements are not signs of weakness; they are the normal state of a living research program that continues to refine its answers to the questions that have driven open economy macroeconomics since the 1960s.