Leonard Levy's classic work examines the circumstances that led to the writing of the establishment clause of the First Amendment: 'Congress shall make no law respecting an establishment of religion. . . .' He argues that, contrary to popular belief, the framers of the Constitution intended to prohibit government aid to religion even on an impartial basis. He thus refutes the view of 'nonpreferentialists,' who interpret the clause as allowing such aid provided that the assistance is not restricted to a preferred church.

For this new edition, Levy has added to his original arguments and incorporated much new material, including an analysis of Jefferson's ideas on the relationship between church and state and a discussion of the establishment clause cases brought before the Supreme Court since the book was originally published in 1986.