Comparative Political Studies XX(X) 1–24 © 2010 SAGE Publications DOI: 10.1177/0010414009355534 http://cps.sagepub.com Unified Government, Bill Approval, and the Legislative Weight of the President Eduardo Alemán 1 and Ernesto Calvo 1 Abstract This article proposes a new approach to measuring the legislative weight of the president and Congress based on the approval of each actor’s legislative agenda.The authors focus on presidential systems where presidents possess both formal authority to introduce their own bills and a variety of prerogatives to influence the passage of legislation. The authors argue that the legislative weight of the president varies over time in response to contextual political variables.After devising a general model to measure changes in the legislative weight of the president vis-à-vis Congress, the authors empirically test their propositions using data from Argentina. The results indicate that the policy and productivity weights of the president actually increase in the absence of unified government. Keywords Congress, divided government, legislative success Most of the comparative research on presidential power published over the past 20 years considers the legislative weight of the president to be fixed and to stem from exogenously granted constitutional authority. We believe, however, 1 University of Houston, Houston, TX Corresponding Author: Eduardo Alemán, University of Houston, Department of Political Science, 447 Philip G. Hoffman Hall, Houston, TX 77204-3011 Email: ealeman2@uh.edu doi:10.1177/0010414009355534 Comparative Political Studies OnlineFirst, published on January 6, 2010 as