Wilson v. Boyce is a United States Supreme Court case that was decided in 1875. The case involved a dispute between two parties over a contract for the sale of a steamboat. The plaintiff, Wilson, had contracted with the defendant, Boyce, to purchase a steamboat for $2,000. Wilson paid the full amount, but Boyce refused to deliver the boat. Wilson then sued Boyce for breach of contract. The Supreme Court held that Boyce was liable for breach of contract. The Court found that the contract was valid and enforceable, and that Boyce had breached it by failing to deliver the boat. The Court also held that Wilson was entitled to damages for the breach, and that Boyce was liable for the full amount of the contract price. The Court's decision in Wilson v. Boyce established the principle that a party who breaches a contract is liable for the full amount of the contract price, regardless of any mitigating circumstances. This principle has been applied in numerous cases since then, and is still an important part of contract law today.

Justice Field delivered the dissenting opinion in Wilson v. Boyce, arguing that the majority's decision was wrongfully decided and should be reversed. He argued that a contract between two parties is binding upon them both, regardless of any subsequent changes to state law or regulations. In this case, he noted that there had been an agreement between Wilson and Boyce for the sale of certain lands which included a provision for payment by installments over time; however, when it came time to make those payments due under the terms of their contract, Boyce refused on account of new laws enacted by Congress after they entered into their agreement. Justice Field asserted that these new laws could not be applied retroactively as they would have no effect on contracts already made prior to their enactment - thus making them voidable at best - and so he concluded his dissent with a call for reversal of the majority's ruling in favor of Boyce.