Understanding the dynamics of lawmaking in the United States is at the center of the study of American politics. A fundamental obstacle to progress in this pursuit is the lack of measures of policy output, especially for the period prior to 1946. The lack of direct legislative accomplishment measures makes it difficult to assess the performance of our political system. We provide a new measure of legislative significance and accomplishment. Specifically, we demonstrate how item-response theory can be combined with a new dataset that contains every public statute enacted between 1877 and 1994 to estimate “legislative importance” across time. Although the resulting estimates and associated standard errors provide new opportunities for scholars interested in analyzing U.S. policymaking since 1877, the methodology we present is not restricted to Congress, the United States, or lawmaking.