This article draws on the debates over evolution in the UnitedS tates to explore efforts to define and defend the boundaries of science. When the first organized opposition to evolution appeared in the early 1920s, antievolutionists insisted that evolution should not be taught because its speculaitve nature placed it outside the boundaries of science. By the last quarter of the century, however, they had largely abandoned that position in favor of arguing that creationism and intelligent design should themselves be regarded as science. This dramatic shift reflected a major reinterpretation of the U.S. Constitution, especially the First Amendment, which states, “Congress shall make no law respecting an establishment of religion”. Until after World War II the U.S. Supreme Court limited the application of this provision to the federal government. That practice began to change in the late 1940s, when the Court began applying First Amendment restrictions against the establishment of religion to the individual states and public school districts by way of the 14th Amendment; by the early 1960s it was asserting a goal of “neutrality” with regard to religion in public education. Because teaching “bad science” does not violate the Constitution, opponents of creationism have embraced the tactic of demonstrating that creation-science and Intelligent Design are essentially religious doctrines — and thus that teaching them in public schools is unconstitutional.