The polarization of political parties in the United States is a well-documented phenomenon. This paper considers polarization of the judicial branch and relates it to the evolution of the parties. In this paper we define polarization specifically as movement from a modal distribution (of votes, attitudes, or decisions) to a bimodal distribution along a liberal-conservative spectrum over time. Using data compiled from 90,000 United States District Court decisions published in the Federal Supplement between 1934 and 2008, we find that the judiciary began to polarize in the 1960s and has remained polarized. We consider a number of competing explanations for the polarization of the district courts, including a top-down view that emphasizes presidential power and a bottom-up view that focuses on the sorting of elites that form the pool of potential judges.