Apostasy (pronounced /əˈpɒstəsi/; from Greek ἀποστασία (apostasia), a defection or revolt, from ἀπό, apo, "away, apart", στάσις, stasis, "stand", "standing") is the formal disaffiliation from, or abandonment or renunciation of a religion by a person.
Apostasy in Christianity 
- The kiss of the apostate was the most bitter earthly ingredient in the agonies which Christ endured.
- Elias Lyman Magoon, reported in Josiah Hotchkiss Gilbert, Dictionary of Burning Words of Brilliant Writers (1895), p. 14.
- Still in the garden shadows art Thou pleading,
Staining the night dews with Thine agony;
But one is there Thy woe and prayer unheeding,
And to their guileless prey
Thy murderers leading, Lord, is it I?
- George Huntingdon, reported in Josiah Hotchkiss Gilbert, Dictionary of Burning Words of Brilliant Writers (1895), p. 14.
Apostasy in Islam 
- Lo! those who disbelieve after their (profession of) belief, and afterward grow violent in disbelief: their repentance will not be accepted. And such are those who are astray.
- The laws of Islam, to which anyone who joins it agrees, forbid someone born a Muslim, or someone who [begins] to believe in Islam [at some point in his life] of his own free will, to rebel against Islam and to move to any other religion...
- Sharia court ruling in Egypt, "Egyptian Court in Controversial Ruling: Christians Who Convert to Islam Cannot Convert Back". MEMRI. August 8, 2007.
- AbuMusa said: Mu'adh came to me when I was in the Yemen. A man who was Jew embraced Islam and then retreated from Islam. When Mu'adh came, he said: I will not come down from my mount until he is killed. He was then killed. One of them said: He was asked to repent before that.
Apostasy in New Religious Movements 
- "The apostate is generally in need of self-justification. He seeks to reconstruct his own past, to excuse his former affiliations, and to blame those who were formerly his closest associates. Not uncommonly the apostate learns to rehearse an 'atrocity story' to explain how, by manipulation, trickery, coercion, or deceit, he was induced to join or to remain within an organization that he now forswears and condemns."
- Bryan Wilson, The Social Dimensions of Sectarianism
- "Others may ask, if the group is as transparently evil as he now contends, why did he espouse its cause in the first place? In the process of trying to explain his own seduction and to confirm the worst fears about the group, the apostate is likely to paint a caricature of the group that is shaped more by his current role as apostate than by his actual experience in the group."
- David Bromley, Anson Shupe, and J.C. Ventimiglia, The Role of Anecdotal Atrocities in the Social Construction of Evil," in Bromley and Richardson, Brainwashing Deprogramming Controversy, p. 156
- "Most former members do not become apostates. They remain — in sociological terms suggested by David Bromley and others — "defectors" (members who somewhat regret having left an organization they still perceive in largely positive terms), or "ordinary leave takers" with mixed feeling about their former affiliation. However ordinary leave takers (and, to some extent, defectors) remain socially invisible, insofar as they do not like or care to discuss their genuine representatives of the former members. In fact, quantitative research shows that even in extremely controversial groups, apostates normally represent less than 15% of former members."
- Massimo Introvigne, Religious Liberty in Europe: Apostate
- "The Lewis and Bromley study became a landmark study in shifting the onus of pathology experienced by former members of new religions from the religions to the coercive activity of the anti-cult movement. In the wake of this study (and other works that confirmed its findings), treating former members as people in need of psychological help has largely ceased. The lack of any widespread expressed need for psychological help by the tens of thousands of former members of new religions in the succeeding decade has itself become the strongest evidence refuting the early sweeping condemnation of new religions as causes of psychological trauma."
- Gordon Melton, Brainwashing and the Cults: The Rise and Fall of a Theory
- "Neither the objective sociological researcher nor the court of law can readily regard the apostate as a creditable or reliable source of evidence. He must always be seen as one whose personal history predisposes him to bias with respect to both his previous religious commitment and affiliations, the suspicion must arise that he acts from a personal motivation to vindicate himself and to regain his self-esteem, by showing himself to have been first a victim but subsequently to have become a redeemed crusader. As various instances have indicated, he is likely to be suggestible and ready to enlarge or embellish his grievances to satisfy that species of journalist whose interest is more in sensational copy than in a objective statement of the truth."
- Bryan R. Wilson, Apostates and New Religious Movements
- "The dramatic import of each apostate's story is reinforced in its significance, to the detriment of objective and ethically neutral enquiry into religious phenomena of the kind undertaken by academic sociologists. Contemporary religious bodies, operating in a context of rapid social change and changing perceptions of religious and spiritual belief, are likely to be particularly susceptible to the disparagement and misrepresentation which occurs through the circulation and repetition of the accounts of apostates."
- Bryan Wilson, Apostates and New Religious Movements
- "Our understanding of leavers has probably been the category most obscured by the polarized cult wars of the twentieth century. Many monographic accounts of specific NRMs notoriously make not attempt to investigate leavers. [..] Investigators are further hampered by the negative attitudes taken by NRM leaders toward any attempt to interview ex-members. Bromley and Johnson among many others have labeled all those who left their NRMs under less than friendly terms "apostates", and this label has been used to cast on the veracity of data collected from them. It has thus been a widespread practice until recently to ignore data gathered from leavers. "
- Benjamin Zablocki and J. Anna Looney in Research on New Religious Movements in the Post-9/11 World, article that appeared in the book New Religious Movements in the 21st Century edited Phillip Charles Lucas & Thomas Robbins (2004) ISBN 0-415-96576-4