Arthur v. Moller 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 Arthur and Moller, in which Arthur agreed to pay Moller a certain amount of money for the use of a certain piece of land. Moller argued that the contract was invalid because it was not in writing, while Arthur argued that the contract was valid because it had been orally agreed upon. The Supreme Court ultimately ruled in favor of Arthur, finding that the contract was valid and enforceable. The Court held that a contract does not need to be in writing in order to be valid, and that an oral agreement between two parties can be just as binding as a written one. The Court also noted that the parties had acted in good faith and that there was no evidence of fraud or misrepresentation. The Court's ruling in Arthur v. Moller established that oral contracts can be just as valid and enforceable as written ones, and that parties can rely on the terms of an oral agreement just as they would a written one. This ruling has been cited in numerous subsequent cases, and has become an important precedent in contract law.

Justice Field delivered the dissenting opinion in Arthur v. Moller, arguing that the majority's ruling was contrary to established precedent and would lead to an absurd result. He argued that a contract for personal services is not assignable under any circumstances, as it involves a special relationship between two parties which cannot be transferred without their consent. Furthermore, he noted that even if such contracts were assignable, they could only be assigned with the consent of both parties involved in the original agreement; thus, since there had been no such mutual assent here, Arthur should have been allowed to enforce his claim against Moller despite having sold his rights to another party. Finally Justice Field concluded by noting that allowing this type of assignment would create uncertainty and confusion in contractual relationships and undermine public confidence in them.