Mahomet v. Quackenbush was a United States Supreme Court case that dealt with the issue of whether a state court had the authority to enforce a contract made between two parties in another state. The case involved a dispute between Mahomet, a resident of New York, and Quackenbush, a resident of New Jersey. Mahomet had contracted with Quackenbush to build a house in New Jersey, but Quackenbush failed to complete the job. Mahomet then sued Quackenbush in a New York court, seeking damages for breach of contract. Quackenbush argued that the New York court did not have jurisdiction over the case, as the contract had been made in New Jersey. The Supreme Court ultimately held that the New York court did have jurisdiction over the case. The Court reasoned that the contract was made in New Jersey, but the breach of contract occurred in New York, and thus the New York court had jurisdiction over the case. The Court also noted that the contract was made with a resident of New York, and thus the New York court had a legitimate interest in protecting the rights of its citizens. The Court's decision in Mahomet v. Quackenbush established that a state court can enforce a contract made in another state, provided that the breach of contract occurred in the state where the court is located. This decision has been cited in numerous subsequent cases, and has become an important precedent in contract law.

Justice Field delivered the dissenting opinion in Mahomet v. Quackenbush, arguing that the Court should not have reversed the decision of the Supreme Court of California. He argued that while it was true that a state law could not take away rights granted by federal laws, this case did not involve such an issue because there were no federal laws granting any right to bring suit against a county for damages caused by its officers or agents. The only question before them was whether California had given citizens such a right and if so, whether they had taken it away with their subsequent legislation. Justice Field believed that since California had given citizens this right through common law principles prior to passing their statute on municipal corporations, then they still retained this power even after passing said statute as long as it did not explicitly repeal or modify those common law principles; which he felt it did not do here. Therefore, he concluded that Mahomet's suit should be allowed to proceed under these common law principles and thus disagreed with his colleagues' decision to reverse the judgment of the Supreme Court of California in favor of Quackenbush