Rapid technological changes pose serious challenges for the Environmental Protection Agency (“EPA”) and other regulators charged with protecting human health and the environment. These changes can result not only in significant harms, but also in the entrenchment of new technologies that can be difficult to undo should the need arise. In urgent circumstances, agencies often must act quickly, but they face an increasingly ossified rulemaking process. The Administrative Procedure Act’s (“APA”) “good cause” exception to notice-and-comment rulemaking offers the most promising option for a swift and effective response. Empirical analysis of EPA’s use of that exception demonstrates that, contrary to concerns regarding potential agency abuse, EPA has exercised restraint in invoking the exception. Going forward, EPA should consider more aggressive use of the exception to respond to urgencies resulting from rapid technological developments and environmental changes. In justifying an expedited approach, EPA can make explicit reference to congressional inaction on an issue, the generally protracted nature of contemporary rulemaking, and the particular delays that the agency has encountered in ordinary rulemaking.