The Free Exercise Clause is a component of the Bill of Rights in the United States Constitution that states that the government cannot interfere with the exercise of religious faith. It is paired with the Establishment Clause in the First Amendment, in the section that says "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof." This clause has been interpreted to mean that the religious freedoms of people in the United States are protected and that the government cannot be involved in the practice and expression of faith.
Under the clause, Congress cannot pass a law that would have the effect of interrupting the practice of religious faith. For example, Congress cannot ban Communion, a rite in some Christian sects, because this would be a violation of the First Amendment. The Establishment Clause ensures that the government cannot establish its own religion or give a particular religion preference, and it cannot mandate when and how people practice their faith.
There are some limits to the interpretation of the Free Exercise Clause. While Congress cannot target a specific religion with a law, it is generally accepted that, if a law has the unintended effect of limiting religious practice, it will withstand challenge. For example, murder is illegal. If people tried to argue that human sacrifice was a component of their religious practice and challenged murder laws under this clause, the courts would rule that, because these laws are not intended to limit the expression of faith, they should be allowed to stand.
Another component of challenges is the concept of compelling interest. The government is allowed to pass laws that have the effect of limiting religious practices if it has a compelling interest to do so. Murder laws are an excellent example of compelling interest, and challenges to polygamy laws have also stood up in court. On the other hand, attempts to outlaw the religious use of peyote by Native Americans have failed because the courts have ruled that the government has no compelling use in regulating the religious use of drugs.
Freedom of religion is very important to many people in the United States. Periodic challenges to policy and the law have relied on the Free Exercise Clause to argue that the boundaries of freedom of religious faith were overstepped. The interpretation of this clause has fluctuated throughout American history, depending on the makeup of the courts and general social attitudes.