The idea of America as politically polarized--that there is an unbridgeable divide between right and left, red and blue states--has become a clichA©. What commentators miss, however, is that increasing polarization in recent decades has been closely accompanied by fundamental social and economic changes--most notably, a parallel rise in income inequality. In Polarized America, Nolan McCarty, Keith Poole, and Howard Rosenthal examine the relationships of polarization, wealth disparity, immigration, and other forces, characterizing it as a dance of give and take and back and forth causality. Using NOMINATE (a quantitative procedure that, like interest group ratings, scores politicians on the basis of their roll call voting records) to measure polarization in Congress and public opinion, census data and Federal Election Commission finance records to measure polarization among the public, the authors find that polarization and income inequality fell in tandem from 1913...