Lockups are agreements made by insiders of stock-issuing firms to abstain from selling shares for a specified period of time after the issue. Brav and Gompers (2003) suggest that lockups are a bonding solution to a moral hazard problem and not a signaling solution to an adverse selection problem. We challenge this conclusion theoretically and empirically. In our model, insiders of good firms signal by putting and keeping (locking up) their money where their mouths are. Our model yields two comparative statics: lockups should be shorter when a firm is i) more transparent and/or ii) more risky. Using a sample of 4,013 initial public offerings and 3,279 seasoned equity offerings between 1988 and 1999, we find empirical support for our theoretical predictions.