Transportation Company v. Downer was a case heard by the United States Supreme Court in 1870. The case involved a dispute between the Transportation Company and Downer, a passenger on one of the company's steamboats. Downer had purchased a ticket from the company, but was denied passage on the boat due to overcrowding. Downer then sued the company for breach of contract, claiming that the company had failed to provide him with the transportation he had paid for. The Supreme Court ruled in favor of Downer, finding that the company had breached its contract with Downer by failing to provide him with the transportation he had paid for. The Court held that the company was liable for damages, and ordered it to pay Downer the full amount of his ticket price. The Court also held that the company was liable for any additional damages that Downer may have suffered as a result of the breach of contract. The ruling in Transportation Company v. Downer established an important precedent in contract law, establishing that companies are liable for damages when they fail to fulfill their contractual obligations. This case also established the principle that companies must provide passengers with the transportation they have paid for, regardless of any overcrowding or other issues that may arise.

In Transportation Company v. Downer, the Supreme Court was tasked with determining whether a contract between two parties that had been partially performed could be enforced by one party against the other. The majority opinion held that contracts are not enforceable when they have only been partially performed, and thus found in favor of Downer. However, Justice Field dissented from this opinion on the grounds that it would lead to injustice for those who had already completed their part of an agreement but were unable to receive any benefit from it due to its partial performance. He argued that such a ruling would encourage dishonesty among contracting parties as well as discourage people from entering into agreements at all if there was no guarantee of enforcement should either side fail to fulfill their obligations under the contract. As such, he concluded that contracts should still be enforceable even when only partially performed so long as both sides had received some benefit or detriment from them prior to termination.