The Supreme Court has wide discretion to choose the cases it will decide. These choices matter, as they both shape and are shaped by our national social, political, and economic discourse. So how does the Court exercise its discretion? The Supreme Court’s rules explain that it may hear any case “important” enough for it to decide. Unsurprisingly, commentators have criticized this standard as “murky,” “cryptic,” “hopelessly indeterminate,” and even “intentionally vague.” But the Court has, in fact, said more about how it decides whether to grant review. We simply must look past the terse text of the Supreme Court Rules and to the Court’s merits opinions. These decisions sometimes offer a brief yet informative description of the decision to grant review. In these oft-overlooked statements, the Court sometimes suggests that review is founded on concerns for comity among the branches, or aimed at structuring intrajudicial authority, among other rationales. Viewed in aggregate, these statements are suggestive of trends in the exercise of the Court’s docket-setting discretion. In this article, I present a text and data analysis of thousands of Supreme Court opinions describing the reason for granting review, collectively illuminating which cases are important enough to merit certiorari. This view into the Court’s agenda-setting process is revealing. We can begin to discern which cases earn the Court’s attention, and how the Court’s priorities change over time. I find, for example, that the Court’s docket shifts in response to large events (e.g., depressions and wars) and to significant political developments (e.g., landmark legislation). And, perhaps more concerning, I also find that individual appointments shape the Court’s docket. The Court should thus better explain its decisions to grant review in the mode of a common law of certiorari. Doing so can improve the interbranch dialogue over judicial reform and instill greater confidence in our Supreme Court.