Scientology claims that it is fully compatible with all existing major world religions and that it does not conflict with them or their religious practices. There are, however, major differences in the beliefs and practices between Scientology and most religions, especially the major monotheistic religions. Members are not allowed to engage in other treatments or mental therapies (even if religious). However, some ministers from other churches have adopted some Scientology secular programs. 
Church of England
The Church of England complained in March 2003 to the Advertising Standards Authority about the Church's advertising poster promoting Narconon—the drug rehabilitation program based on the works of L. Ron Hubbard. The poster claimed "250,000 people salvaged from drugs." The Church of England Diocese of Birmingham challenged the claim. Upholding the complaint, the ASA considered that, "without clarification, readers were likely to interpret the claim '250,000 people salvaged from drugs' to mean that 250,000 people had stopped being dependent on street or prescription drugs because of Scientology. The Authority "accepted that more than 250,000 people had undertaken the Church's Drug Purification and Drug Rundown programs, which were designed to free people from the effects of taking drugs," but "the Authority understood that, within Scientology, the concept of 'drug use' referred to a variety of behaviors that ranged from heavy use of street drugs to occasional ingestion of alcohol or prescription medicines and exposure to chemical toxins."
The Diocese of Birmingham objected to Scientology using space in the community center alloted for religious use. The Diocese pointed out that Scientology does not have religious status in the UK: "Scientology has rightly been refused recognition as a religion by the UK Charity Commissioners" in the words of a Diocese spokesman. The Diocese also stated that "as much a religion as a dog is a vegetable."
Greek Orthodox Church
Maximos Aghiorgoussis, the bishop of the Greek Orthodox Archdiocese of America in Pittsburgh, has stated that Scientology is not in fact a "church", but rather a gnostic/theosophical system of thought. He went on to say that there are at least six serious points of contention between the two groups, including:
- the pantheistic nature of Scientology,
- Scientology's contention that the individual is a noncorporeal, semi-divine "thetan," which runs contrary to the Greek Orthodox view that the individual is both body and soul and, while created in the image of God, not a god himself,
- Scientology's belief that the universe is the "result of a game of the thetans", rather than the account of the Creation according to Genesis,
- Scientology's belief that the thetan can be saved through the clearing of its engrams, which differs from the Christian view of salvation being only through Christ, and
- Scientology's view that death is "of no consequence and significance because death is repeated innumerable times", which runs contrary to the Christian view of a single physical incarnation.
He also states that "Scientology teaches that psychic powers, (evil) spirits and out-of-body events can be used in order for the thetans to rediscover their true powers. This for us Christians means that Scientology uses the occult (spiritism). The son of L. Ron Hubbard admitted that "black magic is the inner core of Scientology." And Ron Hubbard himself confessed that "a spirit entity guided him throughout his life." Finally, a good number of scholarly researchers have verified the occult nature of Scientology." He goes on to say that, in spite of Scientology's claims to enhance mental health, that many people have already been damaged by Dianetics. Calling upon what he describes as "unclean spirits", the inexperience of those who do auditing cause "hallucination, irrational behavior, severe disorientation, strange bodily sensations, physical and mental illness, unconsciousness, and suicide. Hubbard admitted most of the above hazards, 'although he maintained that they occurred only through misapplication of the technology of Scientology'". 
Russian Orthodox Church
The Lutheran Church in Germany has criticized Scientology's activities and doctrines, along with those of several other religious movements. According to the U.S. State Department's 2004 Country Reports on Human Rights Practices, "The Lutheran Church also characterizes The Church of Jesus Christ of Latter-day Saints (Mormons), the Jehovah's Witnesses, the Church of Christ, Christian Scientists, the New Apostolic Church, and the Johannish Church as 'sects,' but in less negative terms than it does Scientology."
Roman Catholic Church
The Roman Catholic Church has not made official doctrinal pronouncements specifically related to Scientology, however Cardinal Marc Ouellet stated "Scientology is something else. For me, this community is not a Church". Certain beliefs that are widely associated with Scientology, such as reincarnation, are specifically rejected by the Catholic Church as being incompatible with Catholic belief and practice. Scientology is also, according to a number of religious scholars, a form of gnosticism, which would make it hard to reconcile with Roman Catholicism and other denominations that regard gnosticism as a heresy.
Scientology's claim of religious compatibility to entry-level Scientologists is soon modified by the additional teaching that the various levels of spiritual process which can be reached through Scientology are more advanced than those attainable in other religions. The major monotheistic religions and Scientology share the claim of Universality of their belief system which precludes compatibility in the view of most scholars. Critics point out that, within Scientology, "spiritual abilities" tends to be synonymous with "mystical powers" rather than with "inner peace." Hubbard himself cautioned against the unwise or improper use of powers in his book History of Man.
In its application for tax-exempt status in the United States, the Church of Scientology International states:
|“||Although there is no policy or Scriptural mandate expressly requiring Scientologists to renounce other religious beliefs or membership in other churches, as a practical matter Scientologists are expected to and do become fully devoted to Scientology to the exclusion of other faiths. As Scientologists, they are required to look only to Scientology Scriptures for the answers to the fundamental questions of their existence and to seek enlightenment only from Scientology.||”|
Hubbard sometimes identified himself with Maitreya (Metteya in Pali), a prophesied Buddha of the future. This identification is made most strongly in his 1955–1956 poem Hymn of Asia, which begins with the line "Am I Metteyya?" and emphasizes certain traits of Hubbard that the editors of the publication said matched traits predicted by the "Metteya Legend," such as Metteya appearing in the West, having golden hair or red hair (Hubbard was red-haired), and appearing in a time of world peril, with the earliest of the predicted dates for his return being 2,500 years after Gautama Buddha, or roughly 1950. According to sociologist Stephen A. Kent, however, the traits which the editors say are predicted by the "Metteya Legend" either are not actually present in the Buddhist texts or in some cases are contradicted by the texts: instead of coming at a time of world peril, for instance, the predictions about Maitreya say he will be born to royalty whose domain is "mighty and prosperous, full of people, crowded and well fed," and rather than having hair "like flames," Kent says that the texts predict curly black hair for the Maitreya.
The revealed beliefs in Scientology at higher levels become increasingly contradictory with the world's major religions. The concept of past lives in Scientology is at odds with Judaism, Christianity and Islam. Beliefs concerning the origins and age of the Earth, the root of evil, and the nature of man make it impossible to uphold the beliefs of most other religions while also being a Scientologist. Hubbard claimed that Islam was the result of an extraterrestrial memory implant, called the Emanator, of which the Kaaba is supposedly an artifact. Mainstream religions, in his view, had failed to realize their objectives: "It is all very well to idealize poverty and associate wisdom with begging bowls, or virtue with low estate. However, those who have done this (Buddhists, Christians, Communists and other fanatics) have dead ended or are dead ending."
The section of the Fishman Affidavit pertaining to Operating Thetan level VIII put forward that Hubbard said that Jesus was a pederast. The Church of Scientology had consistently held this section of the Fishman Affidavit to be a forgery. However, in a recent court case the Church of Scientology identified this section as material they hold the copyright to.
- Steve Bruce: Cathedrals to cults: the evolving forms of the religious life. In: Paul Heelas (Hrsg.): Religion, Modernity, and Postmodernity, Blackwell, Oxford 1998, pp. 19-35, 23.
- HCO Policy Letter 15 December 1965R Issue I revised 25 July 1987, STUDENT'S GUIDE TO ACCEPTABLE BEHAVIOR. Guideline "#14. Do not engage in any rite, ceremony, or any similar religious treatment or mental therapy while on course without the express permission of the Director of Training."
- Scientology awards reach out to black community ROBERT FARLEY, St. Petersburg Times, February 18, 2006
- Sedensky, Matt (2007-08-25). "Unlikely allies". AP. Knoxville News Sentinel. http://www.knoxnews.com/news/2007/aug/25/Unlikely-allies/. Retrieved 2007-08-30.
- Advertising Standards Authority record of successful Church of England complaint about Narconon advertisement
- Cartledge, James (2004-04-24). "Church anger at 'cult' space". Evening Mail. http://icbirmingham.icnetwork.co.uk/0100news/0100localnews/tm_method=full%26objectid=14177182%26siteid=50002-name_page.html. Retrieved 2007-08-30.
- "The challenge of metaphysical experiences outside Orthodoxy and the Orthodox response" at ProQuest
- "Russian Orthodox Targets 'Totalitarian Sects'" at Zenit News AgencyArchive copy at the Internet Archive Wayback Machine
- "2004 Country Report on Human Rights Practices in Germany" at United States Department of State
- Bussières, Ian (February 5, 2009). "Scientologie: "Ce n'est pas une Église" - Mgr Ouellet". Le Soleil (Power Corporation of Canada). http://www.cyberpresse.ca/le-soleil/actualites/societe/200902/04/01-824289-scientologie-ce-nest-pas-une-eglise-mgr-ouellet.php. Retrieved 2009-02-17.
- Derakhshani, Tirdad (2005-07-03). "Spirituality through therapy". The Philadelphia Inquirer. http://www.philly.com/mld/inquirer/news/special_packages/sunday_review/12042623.htm. Retrieved 2006-07-01.
- Response to Final Series of IRS Questions Prior to Recognition of Exemption Under Section 501(c)(3) As a Church, October 1, 1993
- Kent, Stephen A. (1996). "Scientology's Relationship With Eastern Religious Traditions". Journal of Contemporary Religion 11 (1): 21. doi:10.1080/13537909608580753. http://www.arts.ualberta.ca/~skent/Linkedfiles/Scientology's%20Relationship%20With%20Eastern%20Religious%20Traditions%20.htm. Retrieved 2007-03-31.
- Hubbard, HCO PL of January 21, 1965
- Karin Spaink. The Fishman Affidavit: introduction. Retrieved 2008-02-29. 
- Some or all of this article is forked from Wikipedia. The original article was at Scientology and other religions. The list of authors can be seen in the page history.
- www.sweenytod.com Collection of CoS quotations regarding Christianity
- www.skeptictank.org Collection of CoS quotations regarding Christianity