The Establishment Clause of the First Amendment, "Congress shall make no law respecting an establishment of religion", may be the most contentious and misunderstood provision of the entire United States Constitution. What exactly is an "establishment of religion"? And what is a law "respecting" it?

Many commentators reduce the clause to "the separation of church and state." This implies that church and state are at odds, that the public sphere must be secular, and that the Establishment Clause is in tension with the Free Exercise of Religion Clause. All of these implications misconstrue the Establishment Clause's original purpose. The clause facilitates religious diversity and guarantees equality of religious freedom by prohibiting the government from coercing or inducing citizens to change their religious beliefs and practices.

In Agreeing to Disagree, Nathan S. Chapman and Michael W. McConnell detail the theological, political, and philosophical underpinnings of the Establishment Clause, state disestablishment, and the disestablishment norms applied to the states by the Fourteenth Amendment. In one of the most thorough accounts of the Establishment Clause, Chapman and McConnell argue that the clause is best understood as a constitutional commitment for Americans to agree to disagree about matters of faith.