Feeneyism, also known as the Boston heresy, is a Christian doctrine associated with the Jesuit priest Leonard Feeney. Feeneyism advocates an interpretation of the dogma extra Ecclesiam nulla salus ("outside the Church there is no salvation") which is that only Catholics can go to heaven and that only those baptised with water can go to heaven. Because Feeneyism denies that non-Catholics can go to heaven, and because it opposes the doctrines of baptism of desire and baptism of blood, Feeneyism is considered a heresy by the Catholic Church.

In 1949, the Supreme Congregation of the Holy Office produced a document to correct the errors of Feeney's interpretation. The document stated: "this dogma (extra Ecclesiam nulla salus) must be understood in that sense in which the Church itself understands it." After refusing to recant his claims, Leonard Feeney was excommunicated from the Catholic Church in 1953 by Pope Pius XII, although he later reconciled with the church in 1972, a few years before his death.

Feeney was a Roman Catholic priest and a member of the Jesuit order. He co-founded the group known as the Slaves of the Immaculate Heart of Mary with Catherine Goddard Clarke. Feeney was also the editor of The Point, which ran a mixture of theological and political articles, some of them branded anti-semitic by Feeney's critics. He was described by the ADL as "Boston's homegrown version of Father Charles Coughlin" for his antisemitism.

Robert F. Kennedy, then a Harvard undergraduate, met with Archbishop Richard Cushing of Boston requesting Feeney's removal. In 1949, Cushing declared Feeney's St. Benedict's Center off-limits to Catholics. That same year Boston College and Boston College High School dismissed four of the center's members from the theology faculty for spreading Feeney's views in the classroom.

Around this time, Fr. Feeney began speaking on Boston Common, gathering large crowds of up to 2,000 people to his public meetings, both supporters and hecklers. According to The Harvard Crimson, Feeney declared that in Catholic majority Boston, he wanted to "rid our city of every coward liberal Catholic, Jew dog, Protestant brute, and 33rd degree Mason who is trying to suck the soul from good Catholics and sell the true faith for greenbacks". Feeney would frequently throw visceral barbs back at his hecklers, describing them as "sexually degenerate, fairy, lewd, obscene, dirty, filthy, rotten, pawns, pimps, and frauds".

On 4 February 1953, the Holy Office declared him excommunicated "on account of grave disobedience to Church Authority, being unmoved by repeated warnings". The Slaves of the Immaculate Heart of Mary later split in two, one of which became the Still River Branch, in good standing with the Catholic Church; the other is a schismatic group that holds to Feeney's views on Salvation.

Decades later, Feeney reconciled with the Catholic Church in 1972 without any recantation from his part.

Feeney's interpretation of the doctrine extra Ecclesiam nulla salus ("outside the Church there is no salvation") is that only Catholics can go to heaven and that only those baptised with water can go to heaven. As such, Feeneyism opposes the doctrines of baptism of desire and baptism of blood as well as the view that non-Catholics can go to heaven. Feeney rejected what was the definition of the Catholic Church of baptism of desire at the time, i.e. the idea that people who openly affiliated with the Catholic Church as well as those spiritually linked to the Catholic Church through an implicit desire could be saved.