The exact phrase “separation of church and state” does not appear in the U.S. Constitution; the core constitutional basis is the First Amendment’s clause that says, “Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof.”

Where it comes from

The phrase is usually traced to Thomas Jefferson’s 1802 letter to the Danbury Baptist Association, where he described a “wall of separation between Church & State.”

What the Constitution says

The relevant text is in the First Amendment, especially:

  • The Establishment Clause , which bars government from establishing an official religion.
  • The Free Exercise Clause , which protects religious practice from government interference.

Why people say it this way

In modern use, “separation of church and state” is shorthand for the idea that government should not promote or control religion, even though that exact wording is not in the Constitution.

TL;DR: It’s not a direct constitutional quote ; it’s a phrase that summarizes the First Amendment’s religion clauses.