In Left Turn: How Liberal Bias Distorts The American Mind, Tim Groseclose argues that media effects play a crucial role in American politics. His case rests on three arguments: (1) that journalists tend overwhelmingly to be liberal rather than conservative; (2) that their innate political bias slants their views in empirically measurable ways; and (3) that this bias fundamentally shapes American politics, by bringing US citizens further to the left than they would naturally be. According to Groseclose, in a world where media bias did not exist, American citizens would on average hold views close to those of Ben Stein or Bill O'Reilly. In such a world, John McCain would have defeated Barack Obama by a popular vote margin of 56%—42% in the 2008 presidential election. In making these claims, Groseclose draws on his own research, and on recent media scholarship by both political scientists and economists, making the broader claim that peer-reviewed social science—which seeks to deal with problems such as endogeneity and selection bias—should be the starting point for public arguments about the role of the media. His book, then, is clearly an effort to bring social scientific arguments into mainstream debates. Groseclose makes no secret of his conservative political leanings—but recent books from left-leaning political scientists such as Jacob Hacker and Paul Pierson are equally unapologetic. It is at least plausible that political scientists' typical unwillingness to engage directly in political arguments has weakened the discipline's capacity for public engagement. In this symposium a diverse group of contributors have been invited to engage with Groseclose's arguments in ways that bring together specific empirical and/or theoretical points and arguments aimed at the broader “political science public sphere” that Perspectives on Politics seeks to nurture. Contributors were asked to consider these five questions: (1): How do we best measure media effects? (2): If media bias exists, what are its plausible sources? (3): Can one use work on media effects to determine what people's views would be in the absence of such bias? (4): Do you agree that American politics is insufficiently representative, and if so what do you consider the primary sources of this problem? (5): What kinds of political and/or media institutions or practices might enhance democratic discourse?—Henry Farrell, Associate Editor