George Tsebelis is Anatol Rapoport Collegiate Professor, Department of Political Science, University of Michigan. He is the author of numerous articles on political institutions. His articles have appeared in professional Journals as American Political Science Review, British Journal of Political Science, Rationality and Society and Journal of Theoretical Politics. He is the author of "Nested Games: Rational Choice in Comparative Politics" (University of California Press, 1990), Bicameralism (with Jeanette Money; Cambridge University Press, 1997), and Veto Players (Princeton University Press, 2002). Bjørn Erik Rasch, Professor, Department of Political Science, University of Oslo. He has written numerous articles on parliaments, and has published nine books (in Norwegian). The most recent one studies parliamentary government and constitutional reforms (Kampen om regjeringsmakten, Fagbokforlaget 2004). His English language articles have appeared journals as Legislative Studies Quarterly, Public Choice, European Journal of Political Economy and Scandinavian Political Studies. Rasch was member of a Constitutional Commission appointed by the Norwegian parliament in late 2003 to review and modernize the Court of Impeachment. He also was member of a committee who designed a new electoral system for the Sami Parliament in Northern Norway. From 2005 Rasch has headed and coordinated the study programs in political science at the University of Oslo.