The role of law clerks at the United States Supreme Court has long been a source of curiosity among observers and scholars alike. Of particular interest are what characteristics determine which applicants are selected to clerk and what influence clerks have on the justices' decision making. Using a two-part framework that identifies information asymmetries, where clerks possess relevant information that they can transmit to their justices, and conditions under which this information leads a justice to learn about policies' impact, I uncover evidence of a causal mechanism by which clerks wield systematic influence over the justices' decision making. I show that information clerks convey that is derived from their ideological preferences and from their experiences and socialization influences their justices' votes on the merits. In the concluding chapter, I argue that these findings shed light on the broader class of principal-agent relationships of which the justice-clerk dynamic is an example and discuss how law clerks pose an opportunity for scholars to learn how principals acquire and use information from their advisors.