Since the creation of the euro, capital flows among member countries have been large and volatile. Motivated by this fact, I provide a theory connecting the exchange rate regime to financial integration. The key feature of the model is that monetary policy affects the value of collateral that creditors seize upon default. Under flexible exchange rates, national governments can expropriate foreign creditors by depreciating the exchange rate, which induces investors to impose tight constraints on international borrowing. Creating a monetary union, by eliminating this source of currency risk, increases financial integration among member countries. This process, however, does not necessarily lead to higher welfare. The reason is that a high degree of capital mobility can generate multiple equilibria, with bad equilibria characterized by inefficient capital flights. Capital controls or fiscal transfers can eliminate bad equilibria, but their implementation requires international cooperation.

We study optimal monetary policy during times of global scarcity of tradable goods. The optimal monetary response entails a surge in inflation, which helps rebalance production toward the tradable sector. While the inflation costs are fully borne domestically, however, the gains in terms of higher supply of tradable goods partly spill over to the rest of the world. National central banks may thus fall into a coordination trap and implement an excessively tight monetary policy causing an unnecessarily sharp global contraction.

This paper describes a paradox of global thrift. Consider a world in which interest rates are low and monetary policy is constrained by the zero lower bound. Now imagine that governments implement prudential financial and fiscal policies to stabilize the economy. We show that these policies, while effective from the perspective of individual countries, might backfire if applied on a global scale. In fact, prudential policies generate a rise in the global supply of savings and a drop in global aggregate demand. Weaker global aggregate demand depresses output in countries at the zero lower bound. Due to this effect, noncooperative financial and fiscal policies might lead to a fall in global output and welfare.

We provide a Keynesian growth theory in which pessimistic expectations can lead to very persistent, or even permanent, slumps characterized by high unemployment and weak growth. We refer to these episodes as stagnation traps, because they consist in the joint occurrence of a liquidity and a growth trap. In a stagnation trap, the central bank is unable to restore full employment because weak growth depresses aggregate demand and pushes the policy rate against the zero lower bound, while growth is weak because low aggregate demand results in low profits, limiting firms’ investment in innovation. Aggressive policies aiming at restoring growth, such as subsidies to investment, can successfully lead the economy out of a stagnation trap by generating a regime shift in agents’ growth expectations.

What is the role of monetary policy in a bubbly world? To address this question, we study an economy in which financial frictions limit the supply of assets. The ensuing scarcity generates a demand for “unbacked” assets, i.e., assets that are backed only by the expectation of their future value. We consider two types of unbacked assets: bubbles, which are created by the private sector, and money, which is created by the central bank. Bubbles and money share many features, but they also differ in two crucial respects. First, while the rents from the creation of bubbles accrue to entrepreneurs and foster investment, the rents from money creation accrue to the central bank. Second, while bubbles are driven by market psychology, and can rise and fall according to the whims of the market, money is under the control of the central bank. We characterize the optimal monetary policy and show that, through its ability to supply assets, monetary policy plays a key role in the bubbly world. The model sheds light on the recent expansion of central bank liabilities in response to the bursting of bubbles.

We provide a model connecting the global saving glut to productivity growth. The key feature is that the tradable sector is the engine of growth of the economy. Capital flows from developing countries to the United States boost demand for US nontradable goods, inducing a reallocation of US economic activity from the tradable sector to the nontradable one. In turn, lower profits in the tradable sector lead firms to cut back investment in innovation. Since innovation in the United States determines the evolution of the world technological frontier, the result is a drop in global productivity growth.