Is it ensure, insure, or assure?
The principle that government must maintain an attitude of neutrality toward religion. Many view separation of church and state as required by the First Amendment. The First Amendment not only allows citizens the freedom to practice any religion of their choice, but also prevents the government from officially recognizing or favoring any religion.
Note: The relationship between church and state has been extremely controversial since the first settlers arrived in America to escape religious persecution in Europe, and many cases involving the issue have reached the Supreme Court.
Note: Interpretation of the principle has been ambiguous: for instance, the Supreme Court has recently upheld laws prohibiting prayer in the schools but has permitted the construction of Nativity scenes on government property. (See also established church and freedom of religion.)