In the United States, certiorari is most often seen as the writ that the Supreme Court of the United States issues to a lower court to review the lower court's judgment for legal error (reversible error) and review where no appeal is available as a matter of right. Before the Evarts Act, the cases that could reach the Supreme Court were heard as a matter of right, meaning that the Court was required to issue a decision in each of those cases. As the United States expanded in the nineteenth century, the federal judicial system became increasingly strained, with the Supreme Court having a backlog of years. The Act solved these problems by transferring most of the court's direct appeals to the newly created Circuit Courts of Appeals, whose decisions in those cases would normally be final. The Supreme Court did not completely give up its judiciary authority, however, because it gained the ability to review the decisions of the courts of appeals at its discretion through writ of certiorari.
Since the Judiciary Act of 1925, most cases cannot be appealed to the U.S. Supreme Court as a matter of right. A party who wants the Supreme Court to review a decision of a federal or state court files a "petition for writ of certiorari" in the Supreme Court. If the Court grants the petition, the case is scheduled for the filing of briefs and for oral argument.
A minimum of four of the nine Justices are required to grant a writ of certiorari, referred to as the "rule of four." The court denies the vast majority of petitions and thus leaves the decision of the lower court to stand without review; it takes roughly 80 to 150 cases each term. In the most recently-concluded term, for example, 8,241 petitions were filed, with a grant rate of approximately 1.1%, Cases on the paid certiorari docket are substantially more likely to be granted than those on the in forma pauperis docket. The Supreme Court is generally careful to choose only cases over which the Court has jurisdiction and which the Court considers sufficiently important, such as cases involving deep constitutional questions, to merit the use of its limited resources. See also Cert pool.
The granting of a writ does not necessarily mean that the Supreme Court disagrees with the decision of the lower court. Granting a writ of certiorari means merely that at least four of the Justices have determined that the circumstances described in the petition are sufficient to warrant review by the Court. Conversely, the Supreme Court's denial of a petition for a writ of certiorari is sometimes misunderstood to mean that the Supreme Court approves the decision of the lower court. Such a denial "imports no expression of opinion upon the merits of the case, as the bar has been told many times." Missouri v. Jenkins, 515 U.S. 70 (1995). In particular, a denial of a writ of certiorari means that no binding precedent is created by the denial itself, and that the lower court's decision is treated as mandatory authority only within the region of jurisdiction of that court.
Certiorari is sometimes informally referred to as cert, and cases warranting the Supreme Court's attention as certworthy. One situation where the Supreme Court sometimes grants a writ of certiorari is when the federal appeals courts in two (or more) federal judicial circuits have ruled different ways in similar situations, and the Supreme Court wants to resolve that "circuit split" about how the law is supposed to apply to that similar kind of situation. Issues of this type are often called "percolating issues."
Cert. granted sub nom is an abbreviation of the legal phrase "certiorari granted sub nomine", meaning "judicial review granted, under name", indicating that a petition for certiorari of a case has been granted, but that the court granting certiorari is hearing the case under a different name than the name under which the subordinate courts heard the case. For example, the case of District of Columbia v. Heller was known as Parker v. District of Columbia in the court below.