Lacombe v. Forstall's Sons was a United States Supreme Court case that addressed the issue of whether a contract between two parties was valid. The case involved a contract between the plaintiff, Lacombe, and the defendant, Forstall's Sons, for the sale of a steamboat. Lacombe had agreed to purchase the steamboat from Forstall's Sons for a certain price, but the contract was never signed. The Supreme Court held that the contract was valid and enforceable. The Court reasoned that the parties had agreed to the terms of the contract and had acted in reliance on the agreement. The Court also noted that the parties had exchanged money and goods in reliance on the agreement, and that the contract was supported by consideration. The Court concluded that the contract was valid and enforceable, and that Lacombe was entitled to recover the purchase price of the steamboat from Forstall's Sons.

In Lacombe v. Forstall's Sons, the Supreme Court was asked to decide whether a Louisiana state court had jurisdiction over a case involving an alleged breach of contract between two parties from different states. The majority opinion held that the Louisiana court did not have jurisdiction in this matter because it involved citizens of different states and thus fell under federal law. Justice Field dissented, arguing that the Constitution does not grant exclusive power to Congress to regulate contracts between citizens of different states; rather, he argued that such matters should be left up to individual state courts as long as they do not conflict with any federal laws or regulations. He further argued that since there were no applicable federal laws or regulations in this particular case, then it should be decided by the Louisiana court according to its own rules and procedures for resolving disputes among its own citizens.