Troy v. Evans was a United States Supreme Court case that dealt with the issue of whether a state could constitutionally require a person to take an oath of allegiance to the state in order to hold public office. The case was brought by William Troy, a former mayor of the city of Mobile, Alabama, who had been removed from office for refusing to take the oath. Troy argued that the oath requirement violated his rights under the Fourteenth Amendment of the United States Constitution. The Supreme Court held that the oath requirement was constitutional. The Court reasoned that the Fourteenth Amendment did not prohibit a state from requiring an oath of allegiance to the state as a condition of holding public office. The Court further held that the oath requirement was a reasonable exercise of the state's power to protect its citizens from disloyalty and treason. The Court's decision in Troy v. Evans established that a state could constitutionally require a person to take an oath of allegiance to the state in order to hold public office. The decision has been cited in numerous subsequent cases involving the issue of oaths and public office.

Justice Field delivered the dissenting opinion in Troy v. Evans, arguing that the Court should not have granted a writ of error to review the decision of the Supreme Court of Arkansas. He argued that there was no federal question presented by this case and therefore it did not fall within Congress' power to grant appellate jurisdiction over state court decisions. Furthermore, he noted that even if there had been a federal question present, it would still be inappropriate for this Court to exercise its discretion in granting certiorari because none of those questions were properly raised or decided by either court below. Finally, Justice Field concluded his dissent by noting that while he disagreed with some aspects of the majority's reasoning on certain points, he ultimately believed they reached an appropriate result given their interpretation of applicable law and precedent.