O'Reilly v. Edrington was a United States Supreme Court case that addressed the issue of whether a state court could enforce a contract that was made in another state. The case involved a contract between two parties, O'Reilly and Edrington, in which O'Reilly agreed to pay Edrington a certain sum of money in exchange for Edrington's promise to pay O'Reilly a certain sum of money at a later date. The contract was made in the state of Mississippi, but Edrington sued O'Reilly in the state of Tennessee to enforce the contract. The Supreme Court held that the state of Tennessee could not enforce the contract because it was made in another state. The Court reasoned that the contract was made in Mississippi and was therefore subject to the laws of Mississippi. The Court further reasoned that the state of Tennessee had no authority to enforce the contract because it was not made in Tennessee. The Court concluded that the state of Tennessee could not enforce the contract because it was made in another state. The Court's decision in O'Reilly v. Edrington established the principle that a state court cannot enforce a contract that was made in another state. This principle has been applied in numerous cases since then and has become an important part of contract law.

Justice Field delivered the dissenting opinion in O'Reilly v. Edrington, arguing that the majority had incorrectly interpreted the law and failed to consider relevant facts of the case. He argued that under Louisiana law, a contract was formed when an offer was accepted by both parties, regardless of whether or not consideration had been given. In this case, he believed there was sufficient evidence to show that such a contract existed between O’Reilly and Edrington; therefore it should have been enforced by the court. Furthermore, Justice Field noted that even if no formal agreement had been made between them prior to litigation beginning, they still could have entered into one during trial proceedings as long as both parties agreed upon its terms – which is what happened here according to his interpretation of events. Finally he concluded with saying “the judgment below should be affirmed” because it correctly applied Louisiana law in determining liability for breach of contract on behalf of O’Reilly against Edrington