• Legal doctrine of incorporation: Bill of Rights' restrictions upon the federal government should also apply, in certain circumstances, to the states as well
• First Amendment rights have been incorporated, meaning that both states and the federal government must follow Establishment and Free Exercise Clauses

The legal doctrine of incorporation states that the restrictions and demands placed on the federal government by the Bill of Rights apply selectively to the states as well. Even though these restrictions and demands were initially addressed only to the federal government, they have since been extended to the states by the due process clause of the Fourteenth Amendment. The Fourteenth Amendment declares that the states may not "deprive any person of life, liberty, or property, without due process of law." The Court has held that the protections extended to us under the Bill of Rights are central to our understanding of liberty and therefore "fundamental" to the states' guarantee of due process of law. With regard to the First Amendment, this means that neither the states nor the federal government may pass laws "respecting an establishment of religion, or prohibiting the free exercise thereof."

The Mormon cases of the 1870s and the Cantwell case in 1940 brought the religious clauses of the First Amendment to the attention of the United States Supreme Court. Since then, through a long series of cases, the Court has sought to provide a clear and uniform interpretation of what religious freedom means. How has it done?