Maclay v. Sands 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 a federal prison. The case arose when a prisoner, William Maclay, was held in a federal prison in California. Maclay sought a writ of habeas corpus from the California Supreme Court, claiming that he was being held in violation of the Constitution. The California Supreme Court granted the writ, and the United States Supreme Court was asked to decide whether the state court had the authority to do so. The Supreme Court held that the state court did not have the authority to issue the writ of habeas corpus. The Court reasoned that the writ of habeas corpus was a federal remedy, and that the state court did not have the power to issue such a writ. The Court also noted that the writ of habeas corpus was a remedy that could only be used in cases where the prisoner was being held in violation of the Constitution. Since Maclay was being held in a federal prison, the Court held that the state court did not have the authority to issue the writ.

Justice Field delivered the dissenting opinion in Maclay v. Sands, arguing that the majority's decision was contrary to established precedent and would have a detrimental effect on creditors' rights. He argued that under prior decisions of this Court, when a debtor assigns his property for the benefit of creditors, he does not thereby divest himself of title but merely creates an equitable lien or trust upon it for their benefit; thus, any subsequent purchaser from him takes subject to such lien or trust. In this case, Justice Field noted that there had been no actual transfer by deed from Maclay to Sands - only an agreement between them which did not convey legal title - and therefore Sands could take nothing more than what Maclay already held: namely an equitable interest in the land as trustee for his creditors. As such, Justice Field concluded that Sand's claim should be dismissed because he had acquired no greater right than what existed at law before his purchase.