Spatial models of policymaking have evolved from the median voter theorem through the inclusion of institutional considerations such as political parties, committees, and various voting and amendment rules. Such models, however, implicitly assume that no policy is more effective than another at solving public policy problems and that all proposers are equally capable of advancing proposals. We relax these assumptions by modeling proposal “quality” and the effort needed to make better proposals. The resulting Legislative Effectiveness Model (LEM) offers three main benefits. First, it can better account for policy changes based on the effectiveness or popularity of the status quo, changing our understanding of how to overcome gridlock in polarized legislatures. Second, it generalizes canonical models of legislative politics, such as median voter, setter, negative agenda setting, and pivotal politics models, all of which emerge as special cases within the LEM. Third, the LEM offers significant new empirical predictions, some of which we initially test (and find support for) within the U.S. Congress.