The Securities and Exchange Commission (SEC) Rule 415 (shelf registration) allows eligible firms to register securities that they intend to issue in the next two years. Once the registration is declared effective, firms can enter the market instantaneously. Ineligible issuers, however, are required to notify the SEC at least forty-eight hours before entry. Supporters of the shelf rule contend that the rule provides valuable flexibility in timing issues. The authors examine this contention by comparing the market-timing performance of shelf and nonshelf debt issues. The results indicate that the shelf rule does provide valuable market-timing flexibility. Copyright 1989 by the University of Chicago.