Scholarly research has demonstrated rather conclusively that American political elites have undergone a marked partisan polarization over the past thirty years. There is less agreement, however, as to whether the American electorate is polarized. This review article evaluates the evidence, causes and consequences of polarization on both the elite and mass levels. A marked difference between the two is found. Elites are polarized by almost any definition, although this state of affairs is quite common historically. In contrast, mass attitudes are now better sorted by party, but generally not polarized. While it is unclear whether this potentially troubling disconnect between centrist mass attitudes and extreme elite preferences has negative policy consequences, it appears that the super-majoritarian nature of the US Senate serves as a bulwark against policy outcomes that are more ideologically extreme than the public would prefer. Moreover, a public more centrist than those who represent it has also at times exerted a moderating influence on recent policies.
* Department of Political Science, Vanderbilt University (email: marc.j.Hetherington@vanderbilt.edu). The author wishes to thank Fred Greenstein, Bruce Oppenheimer, Bruce Larson, John Geer, Christian Grose, Suzanne Globetti, Larry Bartels, Barbara Sinclair and Matthew Levendusky for their comments and suggestions, Corey Bike and Jeremiah Garretson for their research assistance, and Robert Luskin for illustrating how a review article should be written.