Religious freedom is one of United States’ major founding myths and it has become a key issue in the public sphere. The First Amendment to the US Constitution states that “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”. Religious freedom is thus a fundamental principle protected by the first part of the Amendment called the free exercise clause while the State is prohibited from interfering with or favoring any religion. However, when a law of generally applicability is seen by an individual or a group as overlapping their religious freedom, going to trial to protect their constitutional right appears in many as the best option. The “case by case” approach by the courts, and in particular by the federal Supreme Court, as well as the lack of a coherent jurisprudence show how difficult and challenging dealing with religious freedom issues are. Indeed, beyond judging facts in the various cases the judges hear, their constant redefinitions of the boundaries of religious freedom have given them a major role in regulating religious matters. In our study, we focus on six such religious groups which have been involved in litigations and most of whom had their case heard by the US Supreme Court, in order to seek an exemption from the law and continue their otherwise illegal religious practice. After a review of the Mormons’ famous polygamy cases in the late 19th century, we move on to analyzing the litigation involving a Brazilian Church (called the Centro Espirto Beneficente Uniao do Vegetal) using an illegal substance in their sacramental tea. The child death cases involving Christian Scientists are also analyzed as they point out the question of the limits of parents’ religious rights when it comes to their children’s health. The issue of parents’ rights is further discussed in the following case studies of the Amish who can have their own community schools since the famous US Supreme Court Yoder decision in 1972, and in the case of the Twelve Tribes who have been facing accusations of child abuse and illegal child labor.