Guinn v. United States, 238 U.S. 347 (1915), was a United States Supreme Court decision that found certain grandfather clause exemptions to literacy tests for voting rights to be unconstitutional. Though these grandfather clauses were superficially race-neutral, they were designed to protect the voting rights of illiterate white voters while disenfranchising black voters.

The 1870 ratification of the Fifteenth Amendment to the United States Constitution barred each state from denying the right to vote on the basis of "race, color, or previous condition of servitude". In response, several Southern states, including Oklahoma, established constitutional provisions designed to effectively disenfranchise African-American voters without explicitly violating the Fifteenth Amendment. In his majority opinion, Chief Justice Edward Douglass White held that Oklahoma's grandfather clause was "repugnant to the Fifteenth Amendment and therefore null and void". The decision had little immediate impact, as Southern legislatures found other methods to disenfranchise blacks.

The Supreme Court of the United States (SCOTUS) is the highest court in the federal judiciary of the United States. It has ultimate and largely discretionary appellate jurisdiction over all federal and state court cases that involve a point of federal law, and original jurisdiction over a narrow range of cases, specifically "all Cases affecting Ambassadors, other public Ministers and Consuls, and those in which a State shall be Party." The Court holds the power of judicial review, the ability to invalidate a statute for violating a provision of the Constitution. It is also able to strike down presidential directives for violating either the Constitution or statutory law. However, it may act only within the context of a case in an area of law over which it has jurisdiction. The Court may decide cases having political overtones but has ruled that it does not have power to decide non-justiciable political questions.

Established by Article Three of the United States Constitution, the composition and procedures of the Supreme Court were initially established by the 1st Congress through the Judiciary Act of 1789. As later set by the Judiciary Act of 1869, the Court consists of the chief justice of the United States and eight associate justices. Each justice has lifetime tenure, meaning they remain on the Court until they die, retire, resign, or are removed from office. When a vacancy occurs, the president, with the advice and consent of the Senate, appoints a new justice. Each justice has a single vote in deciding the cases argued before the Court. When in majority, the chief justice decides who writes the opinion of the court; otherwise, the most senior justice in the majority assigns the task of writing the opinion.

The Court meets in the Supreme Court Building in Washington, D.C. Its law enforcement arm is the Supreme Court Police.