Reed v. McIntyre was a United States Supreme Court case that addressed the issue of whether a state could impose a tax on a non-resident's income from real estate located in the state. The Court held that a state could not impose such a tax, as it would be a violation of the Privileges and Immunities Clause of the United States Constitution. The case arose when the state of Ohio attempted to impose a tax on the income of a non-resident, William Reed, from real estate located in the state. Reed argued that the tax was unconstitutional, as it violated the Privileges and Immunities Clause of the United States Constitution. The Supreme Court agreed, holding that the tax was a violation of the Clause. The Court reasoned that the Clause was intended to protect the rights of citizens of one state to travel and do business in other states, and that the tax would effectively prevent non-residents from doing business in Ohio. The Court's decision in Reed v. McIntyre established that states cannot impose taxes on non-residents' income from real estate located in the state. This decision has been cited in numerous subsequent cases, and has been used to protect the rights of non-residents to do business in other states.

In Reed v. McIntyre, the Supreme Court was asked to decide whether a state court had jurisdiction over a case involving citizens of different states. The majority opinion held that the state court did not have jurisdiction and that the federal courts should hear such cases instead. Justice Field dissented from this decision, arguing that it would be an unconstitutional extension of federal power if Congress were to grant exclusive jurisdiction in these matters to the federal courts. He argued further that there is no constitutional provision which grants Congress authority over any matter concerning two or more states except for those specifically enumerated in Article III Section 2 of the Constitution. Therefore, he concluded, since there is no express delegation by Congress granting exclusive jurisdiction to one tribunal or another on questions between citizens of different states, then each state has concurrent power with respect thereto and may exercise its own judgment as to how best protect its rights and interests without interference from other jurisdictions.