Although the words “separation of church and state” do not appear in the First Amendment, the establishment clause was intended to separate church from state. When the First Amendment was adopted in 1791, the establishment clause applied only to the federal government, prohibiting the federal government from any involvement in religion. By 1833, all states had disestablished religion from government, providing protections for religious liberty in state constitutions. In the 20th century, the U.S. Supreme Court applied the establishment clause to the states through the 14th Amendment. Today, the establishment clause prohibits all levels of government from either advancing or inhibiting religion.
The Supreme Court has cited Jefferson’s letter in key cases, beginning with a polygamy case in the 19th century. In the 1947 case Everson v. Board of Education, the Court cited a direct link between Jefferson’s “wall of separation” concept and the First Amendment’s establishment clause.
