Adger v. Alston was a case heard by the United States Supreme Court in 1872. The case involved a dispute between two parties over the ownership of a slave named Mary. The plaintiff, Adger, claimed that he had purchased Mary from the defendant, Alston, and that Alston had no right to reclaim her. Alston argued that he had only loaned Mary to Adger and that he had the right to reclaim her. The Supreme Court ultimately sided with Adger, ruling that Alston had no right to reclaim Mary. The Court held that the sale of a slave was a valid contract and that Alston had no right to reclaim Mary after the sale had been completed. The Court also held that Alston had no right to reclaim Mary because he had not provided any evidence that he had a legal right to do so. This ruling established that a sale of a slave was a valid contract and that the seller had no right to reclaim the slave after the sale had been completed.

In Adger v. Alston, the Supreme Court was tasked with deciding whether a state court had jurisdiction to hear an appeal from a federal district court's decision in a case involving admiralty law. The majority opinion held that the state court did not have jurisdiction and thus could not hear the appeal. Justice Field dissented, arguing that while it was true that admiralty cases were traditionally heard by federal courts, there was no reason why states should be barred from hearing such appeals if they chose to do so. He argued further that allowing states to exercise their own discretion in this matter would provide greater access for litigants seeking justice and help ensure uniformity of decisions across jurisdictions. In conclusion, he believed it would be beneficial for both parties involved if states were allowed some degree of autonomy when dealing with matters related to admiralty law appeals.