Cantwell v. Connecticut was a landmark Supreme Court case decided in 1940 that established the principle of free exercise of religion under the First Amendment, which limits state interference in religious practices. This case involved a Jehovah's Witness, Jesse Cantwell, who was arrested for soliciting donations without a permit, highlighting the tension between state regulation and individual religious expression. The Court ruled that the state's actions violated Cantwell's rights, reinforcing the separation of church and state and the protection of religious freedom.