Roger Williams, a Baptist theologian and founder of Rhode Island, originated the concept of a separation between church and state. In 1644, he wrote in The Bloody Tenent of Persecution, "[a] hedge or wall of separation between the garden of the church and the wilderness of the world."

In 1802, Thomas Jefferson popularized Williams’ phrase in a letter to Baptists in CT, when he 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.”

In Reynolds v. United States (1879) the Supreme Court stated that Jefferson's comments could be "accepted almost as an authoritative declaration of the scope and effect of the [First] Amendment."

The First Amendment of the Constitution provides that "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof." Article VI specifies that, "no religious Test shall ever be required as a Qualification to any Office or public Trust under the United States."

During Congressional deliberations to amend the Constitution in1789 Madison argued that he understood the proposed amended language to mean that, “Congress should not establish a religion, and enforce the legal observation of it by law, nor compel men to worship God in any manner contrary to their conscience.”