During the twentieth century, and particularly between the 1930s and 1950s, ideas about the nature of constitutional government, the legitimacy of judicial lawmaking, and the proper role of the federal courts evolved and shifted. This book focuses on Supreme Court justice Louis D. Brandeis and his opinion in the 1938 landmark case Erie Railroad Co. v. Tompkins, which resulted in a significant relocation of power from federal to state courts. Distinguished legal historian Edward A. Purcell, Jr., shows how the Erie case provides a window on the legal, political, and ideological battles over the federal courts in the New Deal era. Purcell also offers an in-depth study of Brandeis's constitutional jurisprudence and evolving legal views. Examining the social origins and intended significance of the Erie decision, Purcell concludes that the case was a product of early twentieth-century progressivism. The author explores Brandeis's personal values and political purposes and argues that the justice was an exemplar of neither "judicial restraint" nor "neutral principles," despite his later reputation. In an analysis of the continual reconceptions of both Brandeis and Erie by new generations of judges and scholars in the twentieth century, Purcell also illuminates how individual perspectives and social pressures combined to drive the law's evolution.