Separation of church and state is a concept based in the Establishment Clause, found in the First Amendment of the U.S. Constitution. The Establishment Clause was extended to apply to the states through the Fouteenth Amendment, and prohibits laws dealing with the establishment of religion. Neither the state or federal government may enact laws which aid one or all religions, or give a preference to one religion over another. The Establishment Clause was intended to prohibit the federal government from declaring and financially supporting a national religion.
Some governmental activity related to religion has been declared constitutional by the Supreme Court. For example, providing bus transportation for parochial school students and the enforcement of "blue laws" is not prohibited. There is often tension between application of the Establishment Clause and the Free Exercise Clause, which protects the exercise of religious freedom. Common issues involving the Establishment Clause involve the inclusion of religious symbols in public holiday displays and school prayer, among others.