Porter v. Pittsburgh Bessemer Steel Company was a United States Supreme Court case that addressed the issue of whether a contract between two parties was valid. The plaintiff, Porter, had entered into a contract with the defendant, Pittsburgh Bessemer Steel Company, to purchase a certain amount of steel. The contract was to be paid for in installments, with the first installment due at the time of the contract. Porter paid the first installment, but failed to pay the second installment. Pittsburgh Bessemer Steel Company then sued Porter for breach of contract. The Supreme Court held that the contract was valid and enforceable. The Court noted that the contract was clear and unambiguous, and that the parties had agreed to the terms of the contract. The Court also noted that the contract was supported by consideration, as Porter had paid the first installment. The Court held that the contract was binding on both parties, and that Pittsburgh Bessemer Steel Company was entitled to damages for Porter's breach of the contract.

Justice Harlan delivered the dissenting opinion in Porter v. Pittsburgh Bessemer Steel Company, arguing that the majority had misapplied the law and failed to consider certain facts of the case. He argued that under Pennsylvania state law, a contract was formed when an offer was accepted by both parties with consideration given for it. In this particular case, he believed there were sufficient facts to show that such a contract existed between Porter and Pittsburgh Bessemer Steel Company (PBSC). Furthermore, Justice Harlan noted that PBSC had acted upon its promise by delivering goods as agreed upon in their negotiations; thus showing they intended to be bound by their agreement even though no formal writing existed at the time of delivery. As such, Justice Harlan concluded his dissent stating PBSC should have been held liable for breach of contract since they refused to pay after receiving what they requested from Porter.