Scholarship on whiteness has grown dramatically over the past decade, affecting nu- merous academic disciplines from literary criticism and American studies to history, sociology, geography, education, and anthropology. Despite its visibility and quantity, the genre has generated few serious historiographical assessments of its rise, development, strengths, and weaknesses. This essay, which critically examines the concept of whiteness and the ways labor historians have built their analyses around it, seeks to subject historical studies of whiteness to overdue scrutiny and to stimulate a debate on the utility of whiteness as a category of historical analysis. Toward that end, the essay explores the multiple and shifting definitions of whiteness used by scholars, concluding that historians have employed arbitrary and inconsistent definitions of their core concept, some overly expansive or metaphorically grounded and others that are radically restricted; whiteness has become a blank screen onto which those who claim to analyze it can project their own meanings. The essay critically examines historians' use of W. E. B. Du Bois's reflections on the “psychological wage”—something of a foundational text for whiteness scholars—and concludes that the “psychological wage” of whiteness serves poorly as a new explanation for the old question of why white workers have refused to make common cause with African Americans. Whiteness scholars' assertions of the nonwhite status of various immigrant groups (the Irish and eastern and southern Europeans in particular) and the processes by which these groups allegedly became white are challenged, as is whiteness scholars' tendency toward highly selective readings of racial discourses. The essay faults some whiteness scholarship produced by historians for a lack of grounding in archival and other empirical evidence, for passive voice constructions (which obscure the agents who purportedly define immigrants as not white), and for a problematic reliance upon psychohistory in the absence of actual immigrant voices. Historians' use of the concept of whiteness, the essay concludes, suffers from a number of potentially fatal methodological and conceptual flaws; within American labor history, the whiteness project has failed to deliver on its promises.