The Closed Partisan Mind traces the roots of partisan polarization to psychological closed-mindedness in the electorate and the changing perception of politics created by polarized political leaders and the new media environment. American politics today can be defined by the intense and increasingly toxic divide between Democrats and Republicans. Matthew D. Luttig explores why so many Americans have endorsed this level of political conflict. Luttig illustrates how the psychological need for closure leads people, regardless of whether they identify as Democrat or Republican, to express more polarized political attitudes. This association between closed minds and partisan polarization is a new phenomenon and can be traced to broader changes in American society, such as the creation of ideologically distinct political parties and a fragmented media environment. These developments have simplified politics into a black-or-white, us-versus-them conflict—making politics appeal to those with closed minds. Today, strong partisans do not just cheer for their political party to win elections. Instead, more akin to religious true believers, strong partisans use their affiliation as a means of understanding right and wrong, friend and enemy, true and false. The Closed Partisan Mind reveals that these dynamics have manifested in both a new type of partisanship and a new type of partisan. The emergence of this new closed partisanship illustrates the dangers that polarization has wrought on society, politics, and the minds of Americans.