United States v. Hosmer was a United States Supreme Court case that dealt with the issue of whether a contract between the United States and a private individual was valid. The case involved a contract between the United States and William Hosmer, a private individual, for the construction of a lighthouse. The contract was signed by the Secretary of the Treasury and the Commissioner of the General Land Office, but not by the President. The Supreme Court held that the contract was valid, despite the fact that it was not signed by the President. The Court reasoned that the President had delegated his authority to the Secretary of the Treasury and the Commissioner of the General Land Office, and that the contract was therefore valid. The Court also held that the contract was binding on the United States, and that the United States was obligated to pay Hosmer for his work. This case established the principle that contracts between the United States and private individuals are valid, even if they are not signed by the President.

In United States v. Hosmer, the Supreme Court was asked to decide whether a contract between two parties could be enforced when one of them had been declared insane after signing it. The majority opinion held that the contract was void because an insane person cannot enter into a valid agreement; however, Justice Field dissented from this ruling and argued that insanity should not necessarily invalidate contracts if both parties were aware of the other's mental state at the time they entered into it. He further noted that allowing such agreements would encourage people to take advantage of those with mental disabilities and thus undermine public policy. In conclusion, he believed that in cases where both sides knew about each other's condition prior to entering into a contract, then it should still be enforceable even if one party later became mentally incapacitated or died before fulfilling their obligations under its terms.