Despite paying a great deal of attention to the effects of divided government on legislative outputs, scholars of American politics have surprisingly ignored the potential impact of divided government on bureaucratic regulatory outputs. In this article we argue that divided government should reduce the volume of federal agency rulemaking. We test this hypothesis against a data set covering 21,000 rules from 1983 to 2005. Our study is one of the first to analyze the determinants of federal bureaucratic rulemaking activity across such a long period of time. Our results demonstrate that during periods of divided government, agencies issue fewer rules and fewer substantively significant rules than they do during periods of unified government. These findings suggest that divided government impedes agency rulemaking.