The First Amendment to the United States Constitution is one of the ten original amendments passed as part of the Bill of Rights. It 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." The phrasing of the First Amendment is an example of what political scientists refer to as negative liberty, which means that it restricts what Congress is free to do, rather than the individual. First Amendment rights, like all constitutional rights, apply to all legal citizens of the USA and can be summarized as follows.
The first clause is known as the Establishment Clause because it prohibits the government from making any law that endorses a particular religion over others. The idea of a "separation of church and state" is often used when talking about this clause, as it comes from a letter Thomas Jefferson wrote about the issue. This clause is the reason why there has never been an official church of the United States, even though many other countries had them at the time America was founded.
Next is the Free Exercise Clause, which is meant to protect citizens from laws that would stop them from practicing their religion. However, as with most rights, the Supreme Court has set up certain limitations. It has ruled that the government may still enforce laws that coincidentally interfere with religious practice, as long as the laws themselves are neutral toward religion. For example, a law against polygamy may still be valid as long as it applies to all people and not specifically Mormons (Reynolds v. United States, 1879).
After that, the amendment states that Congress may not pass laws that take away a citizen's freedom of speech. While this is often considered the most important civil liberty, it is also subject to a wide variety of restrictions, as determined by the Supreme Court. For instance, falsely yelling "fire" in a crowded theater is a classic example of how speech can be abused to put people in danger. Hate speech, libel and slander, and inciting riots are also not protected. In general, protection of free speech comes down to whether it is done in an acceptable time, place, and manner. It should be noted that the amount of money a person or group spends is sometimes also considered a form of political speech and has been subjected to various regulations, especially in the area of campaign finance.
Closely related to speech is the freedom of the press. The Supreme Court is almost always extremely tough on laws that attempt to regulate the content of the news. However the FCC still has the power to regulate obscenity on the airwaves and journalists have to give testimony when summoned before grand juries.
The last of the First Amendment rights is stated in the final clause, which protects freedom of peaceful assembly and protest, again, subject to restrictions. The right of assembly includes freedom of association, meaning that groups have a right to meet together with whomever they wish, and laws forcing them to welcome certain people as members are unconstitutional, provided the reason for exclusion is related to the group's cause.