We propose a new theory of suboptimal risk-taking based on contractual externalities. We examine an industry with a continuum of firms. Each firm's manager exerts costly hidden effort. The productivity of effort is subject to systematic shocks. Firms' stock prices reflect their performance...

When should we expect bubbles? Can levered intermediaries bid up risky asset prices through asset substitution? We study an economy with financial intermediaries that issue debt and equity to buy risky assets. Asset substitution alone cannot cause bubbles because it is priced into the...