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We investigate the role of macroprudential policies in mitigating liquidity traps. When constrained households engage in deleveraging, the interest rate needs to fall to induce unconstrained households to pick up the decline in aggregate demand. If the fall in the interest rate is limited by the zero lower bound, aggregate demand is insufficient and the economy enters a liquidity trap. In this environment, households' ex ante leverage and insurance decisions are associated with aggregate demand externalities. Welfare can be improved with macroprudential policies targeted toward reducing leverage. Interest rate policy is inferior to macroprudential policies in dealing with excessive leverage.

We present a model of financial crises that stem from endogenous complexity. We conceptualize complexity as banks' uncertainty about the financial network of cross exposures. As conditions deteriorate, cross exposures generate the possibility of a domino effect of bankruptcies. As this happens, banks face an increasingly complex environment since they need to understand a greater fraction of the financial network to assess their own financial health. Complexity dramatically amplifies banks' perceived counterparty risk, and makes relatively healthy banks reluctant to buy risky assets. The model also features a novel complexity externality.

We theoretically investigate the interaction of endogenous risk intolerance and monetary policy following a large recessionary shock. As asset prices dip, risk-tolerant agents’ wealth share declines. This decline reduces the market’s risk tolerance and triggers a downward loop in asset prices and aggregate demand when the interest rate policy is constrained. In this context, large-scale asset purchases are effective because they transfer unwanted risk to the government’s balance sheet. These effects are sizable when the model is calibrated to match the estimates of aggregate asset demand inelasticity. The COVID-19 shock illustrates the environment we seek to capture.

Belief disagreements have been suggested as a major contributing factor to the recent subprime mortgage crisis. This paper theoretically evaluates this hypothesis. I assume that optimists have limited wealth and take on leverage so as to take positions in line with their beliefs. To have a significant effect on asset prices, they need to borrow from traders with pessimistic beliefs using loans collateralized by the asset itself. Since pessimists do not value the collateral as much as optimists do, they are reluctant to lend, which provides an endogenous constraint on optimists' ability to borrow and to influence asset prices. I demonstrate that the tightness of this constraint depends on the nature of belief disagreements. Optimism concerning the probability of downside states has no or little effect on asset prices because these types of optimism are disciplined by this constraint. Instead, optimism concerning the relative probability of upside states could have significant effects on asset prices. This asymmetric disciplining effect is robust to allowing for short selling because pessimists that borrow the asset face a similar endogenous constraint. These results emphasize that what investors disagree about matters for asset prices, to a greater extent than the level of disagreements. When richer contracts are available, relatively complex contracts that resemble some of the recent financial innovations in the mortgage market endogenously emerge to facilitate betting.

I investigate the effect of financial innovation on portfolio risks when traders have belief disagreements. I decompose traders’ average portfolio risks into two components: the uninsurable variance, defined as portfolio risks that would obtain without belief disagreements, and the speculative variance, defined as portfolio risks that result from speculation. My main result shows that financial innovation always increases the speculative variance through two distinct channels: by generating new bets and by amplifying traders’ existing bets. When disagreements are large, these effects are sufficiently strong that financial innovation increases average portfolio risks, decreases average portfolio comovements, and generates greater speculative trading volume relative to risk-sharing volume. Moreover, a profit-seeking market maker endogenously introduces speculative assets that increase average portfolio risks.

I illustrate the effect of financial innovation on portfolio risks by using an example with risk-sharing needs and belief disagreements. I consider two types of innovation: product innovation, formalized as an expansion of new financial assets; and process innovation, formalized as a reduction in transaction costs. When belief disagreements are large, both types of innovation increase portfolio risks. Moreover, endogenous financial innovation is directed towards speculative assets that increase portfolio risks.

We build a model in which the Fed and the market disagree about future aggregate demand. The market anticipates monetary policy “mistakes,” which affect current demand and induce the Fed to partially accommodate the market’s view. The Fed expects to implement its view gradually. Announcements that reveal an unexpected change in the Fed’s belief provide a microfoundation for monetary policy shocks. Tantrum shocks arise when the market misinterprets the Fed’s belief and overreacts to its announcement. Uncertainty about tantrums motivates further gradualism and communication. Finally, disagreements affect the market’s expected inflation and induce a policy trade-off similar to “cost-push” shocks.

We provide evidence of the stock market consumption wealth effect by using a local labor market analysis. An increase in local stock wealth driven by aggregate stock prices increases local employment and payroll in nontradable industries and in total, with no effect on employment in tradable industries. In a model of geographic heterogeneity in stock wealth, these responses imply an MPC of 3.2 cents per year and that a 20 percent increase in stock valuations, unless countered by monetary policy, increases the aggregate labor bill by at least 1.7 percent and aggregate hours by at least 0.7 percent two years after the shock.

We present a model of investment hangover motivated by the Great Recession. Overbuilding of durable capital such as housing requires a reallocation of productive resources to other sectors, which is facilitated by a reduction in the interest rate. When monetary policy is constrained, overbuilding induces a demand-driven recession with limited reallocation and low output. Investment in other capital initially declines due to low demand, but it later booms and induces an asymmetric recovery in which the overbuilt sector is left behind. Welfare can be improved by ex post policies that stimulate investment (including in overbuilt capital) and ex ante policies that restrict investment.

This article proposes a welfare criterion for economies in which agents have heterogeneously distorted beliefs. Instead of taking a stand on whose belief is correct, our criterion asserts that an allocation is belief-neutral efficient (inefficient) if it is efficient (inefficient) under any convex combination of agents’ beliefs. Although this criterion gives an incomplete ranking of social allocations, it can identify positive- and negative-sum speculation driven by conflicting beliefs in a broad range of economic environments.