Abstract: This article takes a close look at four of the landmark criminal procedure cases of the 1920s and 1930s--Moore v. Dempsey, Powell v. Alabama, Norris v. Alabama, and Brown v. Mississippi. The article claims that it was no fortuity that modern criminal procedure originated in cases involving southern black defendants. For the Supreme Court to assume the function of superintending the state criminal process required a departure from a century and a half of tradition and legal precedent, both grounded in federalism concerns. The Justices were willing to take that leap only in cases of flagrant injustice--cases that by the 1920s and 1930s arose mainly in the South and involved black defendants charged with serious interracial crimes, usually rape or murder. Part I makes three related points about these egregious exemplars of Jim Crow justice, which provided the occasion for the birth of modern criminal procedure. First, the southern state appellate courts and the United States Supreme Court were operating on the basis of different paradigms when they evaluated the fairness of these criminal trials. For the southern courts, the simple fact that these defendants enjoyed the formalities of a criminal trial, rather than being lynched, represented a significant advance over what likely would have transpired in the pre-World War I era. For the United States Supreme Court, on the other hand, criminal trials were supposed to be about adjudicating guilt or innocence, not simply avoiding a lynching. Second, because these southern criminal trials were so egregiously unfair, public opinion in the nation generally supported the Supreme Court's interventions. Thus, these early criminal procedure cases hardly represent the sort of countermajoritarian judicial decisionmaking one often associates with landmark criminal procedure decisions, such as Mapp or Miranda. Third and finally, it seems quite likely that the southern state courts themselves would have intervened to rectify the obvious injustices involved in these cases had the circumstances been slightly different. Southern courts in the post-World War I period were becoming more committed to norms of procedural fairness, even in cases involving black defendants charged with serious interracial crimes. Yet in cases that aroused outside criticism of the South or that posed broader challenges to the system of white supremacy, the southern state courts regressed. Part II evaluates the impact of these Supreme Court decisions, in terms of both the precise issues involved (e.g., black service on juries) and the general treatment of blacks in the southern criminal justice system. It turns out that none of these rulings had a very significant direct impact on Jim Crow justice. This Part will explore some of the factors that explain the general failure of these Supreme Court decisions to affect the actual treatment of black criminal defendants in the South. Yet this Part also suggests that these criminal procedure rulings may have indirectly contributed to the modern civil rights movement by educating blacks about their rights, mobilizing protest in the black community, and rallying support among sympathetic whites who were horrified by revelations of Jim Crow practices at their worst. Part III connects these criminal procedure decisions to broader themes in constitutional and civil rights history, identifying some tentative lessons regarding the nature and consequences of Supreme Court constitutional decisionmaking and the dynamics through which American race relations have changed over time.