What does the Establishment Clause actually prohibit?

The First Amendment opens: “Congress shall make no law respecting an establishment of religion.” Sixteen words, and centuries of dispute over exactly what they forbid. At minimum, the Establishment Clause bars the government from creating an official state church, the way England had the Church of England — that much nobody disputes. The harder question is how far past that it goes. The Supreme Court has at different times read it to prohibit government from favoring one religion over another, from favoring religion over non-religion generally, or from becoming excessively entangled with religious institutions — for example by funding religious schools, sponsoring prayer in public schools, or displaying religious symbols on government property. The Court’s tests for where the line falls have shifted over decades: the three-part Lemon test (1971) asked whether a law had a secular purpose, whether its primary effect advanced or inhibited religion, and whether it created excessive government entanglement with religion; more recent decisions have moved toward a “history and tradition” approach that asks whether a practice is consistent with how government treated religion at the founding. What has not moved is the basic structure: the Establishment Clause restrains what government may do, not what individuals or private groups may do — it sits in the same sentence as the Free Exercise Clause, which protects individuals’ right to practice their own religion. The two clauses together aim at one goal: a government neutral enough that no American needs the state’s approval, or needs to fear the state’s disapproval, for what they believe. This is general information, not legal advice.