Crucial to understanding the behavior of judges and the outputs of courts is the institutional context in which they operate. One key component of courts’ institutional structure is that the judiciary is organized as a hierarchy, which creates both problems and opportunities for judges. For instance, one problem for judges at the top of a hierarchy is how to best exercise oversight of lower court judges, whose decisions are often not reviewed by higher courts. One opportunity is that higher courts can reverse errors by lower courts; another is that, as new legal issues emerge, hierarchy provides opportunities for judges to learn from one another. Scholars of the judicial hierarchy have pursued two broad approaches. The “team perspective” begins by assuming that all judges in a hierarchy have the same values or principles, and thus care only about achieving the correct outcome in a given case. In the team approach, the key problem in adjudication is informational. All judges agree on the correct outcome of a case, conditional on understanding the relevant facts, but may lack this understanding due to resource constraints or informational advantages enjoyed by litigants. The agency approach, by contrast assumes that judges in the hierarchy have differing preferences, and the key problem is how higher courts can ensure compliance by lower courts. Despite these different foundational assumptions, the team and agency approaches have both been employed successfully to study core questions regarding the judicial hierarchy, including: why hierarchy exists; how higher courts can best oversee lower courts; how learning takes place both within and across the levels of the judiciary; and how collegiality influences judicial decision-making. Yet, while our understanding of the judicial hierarchy has greatly increased in recent years, many questions remain, such as how judges learn and how to measure legal doctrine.