This dissertation re-examines the history of the American Liberty League, building upon observations in recent works by Kimberly Phillips-Fein and David Farber that trace the origins of the modern American conservative political movement back to the reaction against the New Deal programs implemented by Franklin Roosevelt. The Liberty League, it is argued here, established a tradition of what I describe as Constitutional conservatism. The Liberty League, established in 1934 with the expressed purpose of "upholding the Constitution," represented the most forceful and coherent contemporary resistance against a trend toward centralization of power in the federal government and the executive branch that took shape during the Progressive Era and was cemented by the New Deal. Historians writing about conservatism in the the U.S. have most often highlighted other explanations for the motivations underpinning the movement, most notably the "racial backlash" thesis, but a theme of Constitutional conservatism can be traced through many of the conservative political organizations that have emerged in the United States since the demise of the Liberty League in 1936. The first chapter discusses the origins of the Liberty League, which to a considerable extent evolved out of the Association Against the Prohibition Movement. In addition to their shared focus on Constitutional issues, the two organizations utilized the same tactics and showed considerable overlap in terms of membership, leadership and financial backing. Leaders of the organization, discussed in a separate chapter, included Jouett Shouse, William Stayton, Al Smith, Raoul Desvernine, along with a number of wealthy industrialists that provided financial backing, including Pierre du Pont, his brother Irénée du Pont, John Raskob and E. F. Hutton. Further chapters examine the activities of the local and state branches of the Liberty League, the League's attempts to coordinate efforts with other organizations professing a desire for upholding the Constitution and analysis of the publications produced and distributed by the Liberty League. While the organization was funded largely by a small group of wealthy individuals with a vested interest in protecting their vast fortunes, the Liberty League devoted itself in practice to arguing in favor of the more strict interpretation of the Constitution that had largely prevailed in the United States before the New Deal era. Of course, the League failed utterly to convince the electorate, as evidenced by the overwhelming electoral triumph achieved by President Roosevelt in 1936, but it's relentless attempts to highlight the perceived excesses of the New Deal helped fill the void left by the virtual absence of any meaningful Republican opposition, perhaps helping to place some limits on the extent of the New Deal and laying the ground work for future generations of conservatives that continue to draw on the theme of Constitutional conservatism in their efforts to turn back some of the advances made by proponents of a more activist federal government during the Twentieth Century. / History