The freedom to practice whatever religion one chooses, without interference from the government, is one of the founding principles of the United States. So it might come as a surprise that this right was not included in the original Constitution. Instead, it was added in 1791 as part of the First Amendment - which also protects freedom of speech, the press, and peaceful protest. But given the importance of religion for so many, it's no surprise that this has become a complex area of the law.
"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."