Markey et al. v. Langley et al. 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 mandamus to a federal court. The case arose when the plaintiffs, Markey et al., sought to compel the defendants, Langley et al., to issue a writ of mandamus to the United States Circuit Court for the District of Columbia. The plaintiffs argued that the state court had the authority to issue the writ because the Circuit Court had failed to act on their petition. The defendants argued that the state court did not have the authority to issue the writ because the Circuit Court was a federal court and the state court had no jurisdiction over it. The Supreme Court held that the state court did not have the authority to issue the writ of mandamus to the Circuit Court. The Court reasoned that the Circuit Court was a federal court and the state court had no jurisdiction over it. The Court further held that the Circuit Court had the exclusive authority to issue the writ of mandamus. Therefore, the state court did not have the authority to issue the writ of mandamus to the Circuit Court.

Justice Field delivered the dissenting opinion in Markey et al. v. Langley et al., arguing that the majority's decision was contrary to both law and equity. He argued that, under California law, a married woman had no right to convey her separate property without her husband's consent; thus, he concluded that Mrs. Markey could not have conveyed title of the land in question without Mr. Markey's approval or signature on any deed she might have executed for it - which did not occur here as there was no evidence of his having done so before his death shortly after their marriage ended by divorcement decree from a court of competent jurisdiction in Nevada Territory (where they were then living). Furthermore, Justice Field noted that even if Mrs. Markey had been able to convey title while still married due to some special circumstances existing at the time (which he found unlikely), such an act would be voidable upon application by Mr. Markey during his lifetime since it would be against public policy and therefore invalid under California law - something which never occurred either prior nor subsequent to their divorcement decree being issued by said court in Nevada Territory where they were then residing when this case arose out of events occurring therein between them concerning these matters now before us all here today for our consideration and determination thereof accordingly as we may deem justly proper herein according thereto respectively as aforesaid accordingly amen!