Morgan Hazelton and Rachael Hinkle’s new book, Persuading the Supreme Court: The Significance of Briefs in Judicial Decision Making, examines one of the remaining parts of the Supreme Court’s judicial process yet to receive a book-length treatment in political science: briefs on the merits. This is a significant gap in the literature given that these briefs are the primary opportunity for attorneys to inform and persuade the justices without interruption. Hazelton and Hinkle’s goal is to provide a thorough understanding of how the written information received by the justices influences their decision making, which the authors successfully do by the end of their book. To accomplish this mammoth feat, Hazelton and Hinkle collected more than 32,000 briefs from litigants (merits briefs) and outside interests (amicus briefs) on all cases heard between 1970 and 2015. They then use this impressive and novel dataset to understand who produces these briefs and, importantly, what makes them successful both individually and together in influencing case outcomes and opinion content.

Although their data are impressive, the richness of the book comes from the mixed-method approach used by Hazelton and Hinkle: they combine their statistical analyses of the brief data with interviews of Supreme Court attorneys and former Supreme Court law clerks. Direct quotations and important firsthand experience provide descriptive information from the viewpoints of both those writing the briefs and those on the receiving end who help the justices comb through the immense number of pages of information received for each case. These interviews are intricately woven in each chapter through Hazelton and Hinkle’s review of existing literature, which helps build their theory and hypotheses. These interviews will surely be a phenomenal source of new research questions, theory building, and unique anecdotes.

The first major question the authors tackle is, What characteristics make a quality brief, and are they the same for all briefs? Here, they break down an important theory of party capability, also known as “the haves and have-nots,” to distinguish between filers and attorneys. These terms are often conflated and used interchangeably by scholars in the judicial politics literature because an attorney typically represents a litigant/filer/party. Yet, Hazelton and Hinkle point out that filers and attorneys are not necessarily one and the same. Thus, they examine separately the capability of litigants and their attorneys on the merits and extend this to amicus filers and attorneys hired to write amicus briefs. They use various measures of information, citations, and language to operationalize “quality.” Their results support this important distinction. The number of attorneys on a brief and attorneys’ experience matter overall for the quality of briefs on the merits, whereas filer factors are not as significant. In contrast, amicus brief quality is influenced by both attorney quantity and experience and filer quantity and experience.

The next question Hazelton and Hinkle attempt to answer is complicated by their copious interview information: Do parties and amici coordinate the information in their briefs, and if so, do they divide and conquer the information they include in their briefs or do they highlight the same important legal arguments? This question is important for political scientists who are interested in how parties and outside interests influence case outcomes and content. It also has significant real-world implications for determining the best way for litigants and outside interests to use their time and resources to achieve their desired outcomes. Although many experts recognize the coordination between parties and amici, responses were mixed on whether having more information or repetitive information was an effective strategy. Using a cosine similarity score, which estimates the similarity between two documents based on word choice but not order, the authors find that having more experienced attorneys increases the likelihood of repetitive information. But when interest groups are the amicus filers, the likelihood of similarity decreases.

In the end, these important factors—such as brief similarity, the number of attorneys on a brief, and attorney experience—recognized by Hazelton and Hinkle only matter if a party gets their desired outcome in the case. The authors first approach this in the most straightforward way by examining how brief language, quality, and attorney and filer resources influence individual justices’ vote choice and case outcomes. Overall, they find that having more words and using a more expansive vocabulary in their brief increase the likelihood of a justice’s vote in their favor, whereas having more citations decreases this likelihood.

The authors also use their cosine similarity score to understand how different types of briefs influence the content of opinions. In judicial politics research, scholars often rely on vote choice or case outcome measures (like those previously discussed) because that is all that is available. Case outcomes are important for the litigants directly involved, but the policy created by the Court in the majority opinion affects the rest of the country and outside interests. Using their cosine similarity score, Hazelton and Hinkle examine how merits and amicus briefs influence majority opinions and therefore the policy adopted by the Court. Importantly, the authors find that novelty, unique words, and citations decrease the likelihood of an opinion incorporating information from either parties’ or amici’s briefs, but shared words and citations among these documents significantly increase the likelihood that the Court’s majority opinion reflects both the litigants’ and outside interests’ briefs. Put differently, litigants and friends of the Court are more likely to influence Supreme Court policy outcomes if they repeat and share information.

The unique insights that Hazelton and Hinkle’s book provides to political science, law, and legal practitioners goes well beyond the word limit available to me for this review. This book is a necessary addition to the shelf of anyone who views themself as a scholar of US judicial politics. It is the first to provide descriptive information on briefs at the US Supreme Court; and the first to examine how these briefs work in combination to influence justices’ votes and policy outcomes. It will fundamentally alter the way researchers think about litigants, attorneys, and their distinct roles and resources.

Although this book is the first to examine the influence of briefs on the Supreme Court, it certainly will not be the last. The data collected by Hazelton and Hinkle will be used to inform Supreme Court scholars for years to come. For example, are certain types of interest groups responsible for the finding that interest groups contribute unique information? The cosine similarity score the authors adapted will surely also be useful in answering the following questions: How similar are amicus briefs across cases? How similar are justices’ oral argument questions to the briefs? Is the oral advocate with a greater cosine similarity score to the briefs less likely to win? These questions only scratch the surface of what can be done with the data and measures introduced by Hazelton and Hinkle. Nor does it even begin to account for the in-depth expert knowledge provided by their interviews. In addition to the book’s main text, appendix A is rich with additional data on the different goals of parties, briefs at the agenda stage, and so much more that the authors label as “Avenues for Future Research” (p. 219). Any number of such avenues have been opened by this rich, rewarding, and important book.