The First Amendment
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.
The First Amendment in the Bill of Rights guarantees freedoms concerning religion, expression, assembly, and the right to petition. It forbids Congress from both promoting one religion over others and also restricting an individual’s religious practices. It guarantees freedom of expression by prohibiting Congress from restricting the press or the rights of individuals to speak freely. It also guarantees the right of citizens to assemble peaceably and to petition their government.
The First Amendment has two provisions concerning religion: the Establishment Clause and the Free Exercise Clause. The Establishment clause prohibits the government from "establishing" a religion. The precise definition of "establishment" is unclear. Historically, it meant prohibiting state-sponsored churches, such as the Church of England.
Religious liberty, also known as freedom of religion, is "the right of all persons to believe, speak, and act – individually and in community with others, in private and in public – in accord with their understanding of ultimate truth." The acknowledgement of religious freedom as the first right protected in the Bill of Rights points toward the American founders' understanding of the importance of religion to human, social, and political flourishing.
The Free Exercise Clause protects citizens' right to practice their religion as they please, so long as the practice does not run afoul of a "public morals" or a "compelling" governmental interest.