A Supreme Court merits brief serves an informational purpose, supplying the justices with a case’s history, legal arguments, and proposed resolution. While providing this information, however, attorneys use their discretion over the briefs’ language to turn these documents into carefully constructed documents of persuasion. Attorneys use the briefs to define the issues on which the Court will decide the case, frame the justices’ perception of it and make arguments designed to help win the case. In a common law system like the United States, where legal precedents are the primary legal building blocks, these early decisions by attorneys can influence the Court's eventual decisions. While many studies examine how Supreme Court opinions expand or restrict the scope of existing law, no such analysis—so far as we know—takes up how litigants themselves present these arguments to the Court in the written brief. This is important because existing norms prevent the Court from addressing issues and topics not formally presented to it by the litigants. In this chapter, we provide an initial look at the use of legal authority in litigant briefs. Using data collected from a random sample of Establishment Clause cases, we compare human and computer-based approaches for identifying both when precedent is used and, more importantly, how it is used by a litigant. We also examine the determinants of whether the Court ultimately follows the arguments offered by a brief.