Ex parte Parks was a United States Supreme Court case that dealt with the issue of whether a state court had the authority to issue a writ of habeas corpus to a prisoner held in federal custody. The case arose when a prisoner, William Parks, was held in federal custody in the state of Texas. Parks filed a petition for a writ of habeas corpus in the state court, claiming that he was being held in violation of the Constitution. The state court granted the writ, and the federal government appealed the decision to the Supreme Court. The Supreme Court held that the state court did not have the authority to issue a writ of habeas corpus to a prisoner held in federal custody. The Court reasoned that the writ of habeas corpus was a federal prerogative, and that the state court did not have the power to interfere with the federal government's authority to detain a prisoner. The Court also noted that the writ of habeas corpus was a fundamental right, and that the state court should not be allowed to interfere with the federal government's exercise of that right. In conclusion, the Supreme Court held that the state court did not have the authority to issue a writ of habeas corpus to a prisoner held in federal custody. The Court reasoned that the writ of habeas corpus was a federal prerogative, and that the state court did not have the power to interfere with the federal government's authority to detain a prisoner. The Court also noted that the writ of habeas corpus was a fundamental right, and that the state court should not be allowed to interfere with the federal government's exercise of that right.

In Ex Parte Parks, the United States Supreme Court was asked to decide whether a writ of habeas corpus should be granted in order for an individual to challenge his conviction and sentence. The majority opinion held that the writ should not be issued because it would interfere with the state court's jurisdiction over criminal matters. However, Justice Field dissented from this decision on two grounds: firstly, he argued that federal courts have concurrent jurisdiction over cases involving violations of constitutional rights; and secondly, he argued that even if they did not have such authority, Congress had given them power to issue writs of habeas corpus when necessary. He concluded by stating that "the liberty of every citizen is too precious a right" for it to be denied without due process under law.