The Lemon Test

Government action violates the Establishment Clause unless it:
1. Has a significant secular (i.e., non-religious) purpose,
2. Does not have the primary effect of advancing or inhibiting religion, and
3. Does not foster excessive entanglement between government and religion.

Note: Not all justices believe that the Lemon Test is the appropriate test to use in reviewing Establishment Clause cases.  Justice Kennedy, for example, focuses on whether the government compelled, directly or indirectly, affirmation of a religion.  Other justices, such as Scalia and Thomas, are of the view that any practice of government that has a long history is virtually immune from Establishment Clause challenge.