At most publicly traded firms, an insider trading policy (ITP) establishes a pre-specified open trading window each quarter when insiders are allowed to trade, which dictates a corresponding “blackout” period in which they are prohibited from doing so. The typical trading window begins 2-3 trading days after the previous quarter’s earnings release and ends approximately 2-3 weeks prior to the end of the next fiscal quarter, resulting in an allowed trading window of about six weeks. These restrictions on insider trading activity potentially provide both protection from legal or regulatory action as well as liquidity and cost of capital benefits (e.g., Fishman and Hagerty, 1992). Although there is substantial variation in the length and timing of these trading windows, little is known about the factors boards consider when determining these constraints. Furthermore, in addition to these pre-specified trading windows and corresponding blackout periods, firms may impose event-specific trading restrictions on insiders (e.g., due to ongoing merger or acquisition negotiations). These “ad hoc blackout windows,” which are undisclosed to the public, are largely unexplored in prior literature.