Crary v. Devlin was a United States Supreme Court case that addressed the issue of whether a state could impose a tax on the transfer of real estate located in another state. The case was brought by the plaintiff, William Crary, who owned real estate in the state of New York. The defendant, John Devlin, was the Collector of Taxes for the state of New Jersey. Devlin had imposed a tax on the transfer of Crary's real estate, which Crary argued was unconstitutional. The Supreme Court held that the tax imposed by Devlin was unconstitutional. The Court reasoned that the tax was a direct burden on interstate commerce, and thus violated the Commerce Clause of the United States Constitution. The Court further held that the tax was an unconstitutional interference with the right of a state to regulate its own internal affairs. The Court's decision in Crary v. Devlin established that a state cannot impose a tax on the transfer of real estate located in another state. This decision has been cited in numerous subsequent cases, and has been used to support the principle that states cannot interfere with the internal affairs of other states.

Justice Harlan delivered the dissenting opinion in Crary v. Devlin, arguing that the majority's decision was contrary to established precedent and would lead to absurd results. He argued that a contract between two parties should be enforced according to its terms unless it is illegal or against public policy. In this case, he noted that there was no evidence of illegality or any other reason why the contract should not be enforced as written. Furthermore, he argued that if contracts could be invalidated based on their perceived fairness or lack thereof, then all contracts would become subject to judicial review and thus unenforceable due to uncertainty over what constituted fair terms for each party involved. As such, Justice Harlan concluded by stating his belief that courts should enforce valid contracts as written without attempting to second-guess whether they are equitable or justifiable under certain circumstances; otherwise contractual agreements will become meaningless and unreliable instruments of commerce in society at large.