This Essay is a contribution to a volume on the influence of Hans Kelsen’s legal theory in over a dozen countries. The Essay offers four explanations for the failure of Kelsen’s pure theory of law to take hold in the United States. Part I covers the argument that Kelsen’s approach failed in the United States because it is inferior to H. L. A. Hart’s brand of legal positivism. Part II discusses the historical context in which Kelsen taught and published in the United States and explores both philosophical and sociological reasons why the legal academy in the United States rejected Kelsen’s approach. Part III addresses the pedagogical obstacles to bringing Kelsen’s Pure Theory into classrooms in the United States. The final section addresses the U.S. legal academy’s continuing resistance to the pure theory of law. The vehemence with which legal scholars within the United States rejected Kelsen’s philosophy of law is best understood as a product of numerous factors, some philosophical, some political and some having to do with professional developments within the legal academy itself. Because the causal significance of philosophical and political opposition to Kelsen’s legal philosophy has been overstated, this Essay supplements those explanatory models with a sociological account of the U.S. legal academy’s rejection of Kelsen’s pure theory of law.