This is the introduction to the revised and updated edition of Conspiracy Theories: Secrecy and Power in American Culture (Minneapolis: University of Minnesota Press, forthcoming 2008). The book challenges the dominant academic and popular approach to conspiracy theories, which views them as a paranoid, extremist expression of marginal groups and individuals that pathologically challenges the basic assumptions of American history and the pluralistic political system of the United States. The book is premised on the contrary proposition that the prevalence of conspiracy theories is neither necessarily pernicious nor external to American politics and culture but instead an integral aspect of American, and perhaps modern and postmodern, life. Not simply an outlying style of American politics, conspiracy theory has always been a significant element of American political rhetoric, with wide-ranging, sometimes salutary effects. Populist concerns about the concentration of public and private power and of foreign control of domestic authority, for example, have long animated American political practice and governance, and are visible in governmental structures (such as the separation of federal powers and federalism) as well as legislative enactments (e.g., antitrust laws). Conspiracy theory is an aspect of the longstanding populist strain in American political culture - an especially intense strain, to be sure, and one that can have violent, racist, and antidemocratic effects (as well as salutary and democracy-enhancing ones) on the political and social order, but a strain that is neither independent from nor necessarily threatening to the country's political institutions or political culture. Rather than seek some underlying cause for the pathological political or cognitive errors that explains conspiracy theories, the book focuses on conspiracy as a cultural practice, a way of interpreting and narrating politics as part of an oppositional individual and collective project. By studying and understanding how conspiracy theory works, how it constitutes an attractive, engrossing, and prevalent means of engaging in politics, the book offers a better way of conceptualizing and responding to conspiracy theories' rise and circulation. In addition to updating and revising the original edition, the revised edition adds an entirely new chapter on conspiracy theories that concern the 9/11 attacks that considers the additional question of how the state - in the form of the 9/11 Commission - responds to radical challenges to its authority.