A phrase that, while not used verbatim in the Bill of Rights, describes one of the clauses of the First Amendment. The actual text is "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof". Often referred to as the Establishment Clause and Free Exercise Clause.

It implies that religion will not be controlled, mandated, or enforced. Usually interpreted to mean that the government will not have any influence on religion. This interpretation is supported by the Letter to the Danbury Baptists written by Thomas Jefferson.

This would also allow freedom from religion, as it is not free exercise if you are not allowed to not participate.

There is often conflict between what one group thinks of as freedom of religion and what another group thinks, due the complexity of life and society. Common conflicts revolve around prayer at graduation and football games, and how various religions are treated in public institutions such as prisons, schools, and government offices.

Somehow they still find reasons to attempt to pass laws to give more freedom to religion, such as the Religious Liberty Protection Act. If laws are needed to give religion freedom, then someone else passed unconstitutional laws.