United States v. Williams was a United States Supreme Court case that addressed the issue of whether the federal government had the authority to prosecute individuals for the interstate transportation of obscene materials. The case involved the defendant, John Williams, who was charged with transporting obscene materials from one state to another in violation of the Comstock Act. The Court held that the federal government did have the authority to prosecute individuals for the interstate transportation of obscene materials, and that the Comstock Act was constitutional. The Court reasoned that the federal government had the power to regulate interstate commerce, and that the transportation of obscene materials was a form of interstate commerce. The Court also held that the Comstock Act was not overly broad or vague, and that it was a valid exercise of the federal government's power to regulate interstate commerce. The Court's decision in United States v. Williams established the federal government's authority to regulate the interstate transportation of obscene materials.

In United States v. Williams, the Supreme Court was asked to determine whether a federal statute criminalizing the distribution of obscene materials through interstate commerce violated the First Amendment right to free speech. The majority opinion held that it did not violate this right and upheld the conviction of John Williams for distributing such material in violation of this law. Justice Harlan dissented from this decision, arguing that Congress had exceeded its authority by attempting to regulate morality under its power over interstate commerce. He argued that obscenity is protected as part of freedom of expression unless it can be shown to cause harm or incite violence; otherwise, he believed any attempt at censorship would amount to an unconstitutional prior restraint on speech and press freedoms guaranteed by the First Amendment. Furthermore, he noted that there were already state laws prohibiting obscenity which could adequately address any issues related thereto without infringing upon these fundamental rights granted by our Constitution.