See also: Law | Censorship
The first ammendment to the constitution (http://www.house.gov/Constitution/Constitution.html) of the United States of America states;
“Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.”
This is upheld by the courts to prevent the government from imposing content restrictions on publications, but there are still limits to free speech.
TakeDown.NET -> “First-Amendment”