Establishment clause, also called establishment-of-religion clause, clause in the First Amendment to the U.S. Constitution forbidding Congress from establishing a state religion. It prevents the passage of any law that gives preference to or forces belief in any one religion.

The First Amendment's Establishment Clause prohibits the government from making any law “respecting an establishment of religion.” This clause not only forbids the government from establishing an official religion, but also prohibits government actions that unduly favor one religion over another.