The relationships among governmental institutions are some of the most studied phenomena in political science. Yet these complex interactions remain largely unexplained due to the difficult task of developing accurate measures that lead to quantifiable tests that enhance explanation and prediction. This work centers on the interactions of United States Supreme Court justices with other political actors. The goal of this dissertation is to better understand the relationship between the Supreme Court and its institutional environment. In short, I ask: What factors affect Supreme Court justices’ voting decisions? I approach this question from several different angles while making use of a unique dependent variable—Yearly Supreme Court justice ideal point. This variable is a variant of the ideal points calculated by Michael A. Bailey of Georgetown University (Bailey, 2007). My empirical models consider the effects of numerous independent variables on this dependent variable. One of the unique aspects of this study is that it considers the effects of a wide variety of factors purported to affect judicial behavior. There are four main theories of judicial decision-making, and my empirical analyses test notions exported from all of them. In designing and testing my models, I draw especially on the developing approach of new institutionalism—an approach to the study of judicial politics that emphasizes the influence of external, non-judicial political actors on judicial behavior. Ultimately this work will show what factors constrain the actions of Supreme Court justices and to what degree they do so. This research has many implications for larger theoretical concerns of political science, specifically formulating questions about the independence of the judiciary and contains relevant questions for democratic theory as well.