Hailes v. Van Wormer was a United States Supreme Court case that dealt with the issue of whether a contract between two parties was valid. The case involved a contract between the plaintiff, Hailes, and the defendant, Van Wormer, in which Van Wormer agreed to pay Hailes a certain sum of money in exchange for the use of Hailes' land. The contract was signed by both parties, but Van Wormer failed to make the payments as agreed. Hailes sued Van Wormer for breach of contract, and the case eventually made its way to the Supreme Court. The Court held that the contract was valid and enforceable, and that Van Wormer was liable for the payments he had agreed to make. The Court also held that the contract was binding on both parties, and that Van Wormer could not avoid his obligations under the contract. The Court's decision in Hailes v. Van Wormer established that contracts are binding on both parties, and that a party who fails to fulfill their obligations under a contract can be held liable for breach of contract. This decision has been cited in numerous cases since, and is an important precedent in contract law.

In Hailes v. Van Wormer, the Supreme Court was asked to decide whether a contract between two parties could be enforced when one of the parties had died before it was fully executed. The majority opinion held that such contracts were not enforceable because they lacked consideration and mutuality of obligation. However, Justice Field dissented from this decision, arguing that there should be an exception for cases where both parties have already performed some part of their obligations under the contract prior to death or other intervening events which prevent full execution. He argued that in these cases, equity should require enforcement since each party has already partially fulfilled their duties and thus provided sufficient consideration for the agreement as a whole. Furthermore, he noted that if courts refused to recognize such agreements then individuals would lack incentive to perform any part of their contractual obligations until all conditions are met - something which would lead to great injustice and uncertainty in commercial transactions