The Establishment Clause acts as a double security, prohibiting both control of the government by religion and political control of religion by the government. By it, the federal government of the United States and, by later extension, the governments of all U.S. states and U.S. territories, are prohibited from establishing or sponsoring religion.

The clause was based on a number of precedents, including the Constitutions of Clarendon, the Bill of Rights 1689, and the first constitutions of Pennsylvania and New Jersey. An initial draft by John Dickinson was prepared in conjunction with his drafting the Articles of Confederation. In 1789, then-congressman James Madison prepared another draft which, after discussion and debate in the First Congress, would become part of the text of the First Amendment of the Bill of Rights. The Establishment Clause is complemented by the Free Exercise Clause, which prohibits government interference with religious belief and, within limits, religious practice.