Paul v. Virginia was a landmark Supreme Court case that established the principle that a state cannot regulate interstate commerce. The case was brought by Paul, a citizen of Virginia, who was denied a license to sell insurance in North Carolina. Paul argued that the North Carolina law violated the Commerce Clause of the Constitution, which gives Congress the power to regulate interstate commerce. The Supreme Court ruled in favor of Paul, holding that the North Carolina law was unconstitutional. The Court held that the Commerce Clause was intended to protect interstate commerce from state interference, and that the North Carolina law was an attempt to regulate interstate commerce. The Court also held that the Commerce Clause was not intended to give states the power to regulate interstate commerce, and that the North Carolina law was an unconstitutional attempt to do so. The decision in Paul v. Virginia was a major victory for the federal government and for the principle of federalism. It established the principle that states cannot regulate interstate commerce, and that the federal government has the power to do so. This decision has been cited in numerous cases since, and has been a cornerstone of federalism in the United States.

In Paul v. Virginia, the Supreme Court was asked to decide whether a state could require an insurance company incorporated in another state to obtain a license before it could do business within its borders. The majority of the court held that states had no power over foreign corporations and that requiring such companies to obtain licenses violated the Privileges and Immunities Clause of Article IV of the Constitution. Justice Field dissented from this opinion, arguing that states have long been able to regulate businesses operating within their borders regardless of where they were incorporated or chartered. He argued further that allowing states to regulate these companies would not interfere with interstate commerce as Congress has exclusive authority over interstate commerce under Article I, Section 8 of the Constitution. Furthermore, he maintained that if Congress did not wish for states to be able to impose licensing requirements on foreign corporations then it should pass legislation prohibiting them from doing so rather than relying on constitutional interpretation by courts alone.