This is a list, in chronological order, of present and past offences to which the Catholic Church has attached the penalty of excommunication; the list is not exhaustive. In most cases these were "automatic excommunications", wherein the violator who knowingly breaks the rule is considered automatically excommunicated from the church regardless of whether a bishop (or the pope) has excommunicated them publicly. However, in a few cases a bishop would need to name the person who violated the rule for them to be excommunicated.
Excommunication is an ecclesiastical penalty placed on a person to encourage the person to return to the communion of the church. An excommunicated person cannot receive any sacraments or exercise an office within the church until the excommunication is lifted by a valid authority in the church (usually a bishop). Previously, other penalties could also be attached. In cases where excommunication is reserved for the apostolic see, only the bishop of Rome (the pope) has the power to lift the excommunication. Before 1869, the church distinguished "major" and "minor" excommunication; a major excommunication was often marked by simply writing, "Let them be anathema" in council documents. Only offences from the 1983 Code of Canon Law still have legal effect in the church.
First Council of Nicaea (325 AD) Any clergy or deacons who leave their church recklessly can be excommunicated if they fail to return to their dioceses.
Council of Saragossa (380) Anyone who continued to receive Holy Communion by hand. Reaffirmed at the Synod of Toledo (440). Ceased to be an offense in the Latin Church in 1969.
First Council of Constantinople (381) All who follow the following heresies: Eunomians, Anomoeans, Arians, Eudoxians, Semi-Arians, Pneumatomachi, Sabellians, Marcellians, Photinians and Apollinarians.
Council of Ephesus (431) Any laity who seek to upset the decisions of the council of Ephesus. Anyone who does not confess that Jesus is God and Mary is the Mother of God. Anyone who does not confess that the Word from God the Father has become flesh in Jesus Christ and is God and man in one flesh. Anyone who divides the hypostatic union of Christ and claims that the two aspects (divine and human) are not united. Anyone who asserts that some aspects of Jesus belong to his human part and others to his divine part, rather than belonging to both together. Anyone who says that Jesus was a God-bearing man and not God in Truth. Anyone who says that the Word from God was the master of Christ and not the same person. Anyone who says that Jesus as a man was activated by the Word of God and clothed with the glory of God, as though it was separate from him. Anyone who says that Jesus ought to be worshipped with the Divine Word. Anyone who says that Jesus' miracles and exorcism were done by the Holy Spirit as an alien power working through him, and not by Jesus' own spirit. Anyone who says that Jesus became our High Priest, but the Word of God did not become our High Priest, or that Jesus' sacrifice was for himself also. Anyone who says that the body of Christ is not the Word of God and is not life-giving. Anyone who does not confess that the Word of God became flesh, suffered, died and was resurrected. Any layperson who composes a new creed, different from the Nicene Creed, for the benefit of converting people. Any laity who follow the teachings of Nestorius or Charisius regarding the nature of Christ. Any laity in the region of Pamphylia who failed to sign the anathema against the Euchites.
Council of Chalcedon (451) People who found monasteries in dioceses without the bishop's approval, monks who do not obey the local bishop's authority or monasteries who accept slaves as monks without receiving permission from the slave's master. Religious and laity who run monasteries, martyrs' shrines or almshouses who do not obey the local bishop's authority. Monks or nuns who marry. If a bishop receives a priest into his diocese who belongs to another diocese, both the priest and the bishop are excommunicated. Those who concoct two natures of the Lord before the union but imagine a single one after the union. Religious or laity who attempt to produce another creed. Religious or laity who assist in a simoniacal ordination (i.e., buying the sacrament of holy orders). Priests or religious who go into military service or politics. Religious or laity who carry off girls under the pretext of cohabitation or who assist in this.