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 establishment clause separates church from state, but not religion from politics or public life. Individual citizens are free to bring their religious convictions into the public arena. But the government is prohibited from favoring one religious view over another or even favoring religion over non-religion.

Our nation’s founders disagreed about the exact meaning of “no establishment” under the First Amendment; the argument continues to this day. But there was and is widespread agreement that preventing government from interfering with religion is an essential principle of religious liberty. All of the Framers understood that “no establishment” meant no national church and no government involvement in religion. Thomas Jefferson and James Madison believed that without separating church from state, there could be no real religious freedom.

The first use of the “wall of separation” metaphor was by Roger Williams, who founded Rhode Island in 1635. He said an authentic Christian church would be possible only if there was “a wall or hedge of separation” between the “wilderness of the world” and “the garden of the church.” Any government involvement in the church, he believed, corrupts the church.

Then in 1802, Thomas Jefferson, in a letter to the Danbury Baptist Association, wrote: “I contemplate with sovereign reverence that act of the whole American people which declared that their legislature should ‘make no law respecting an establishment of religion, or prohibiting the free exercise thereof,’ thus building a wall of separation between Church and State.”

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.