According to its literature: "Scientology is a religion that offers a precise path leading to a complete and certain understanding of one's true spiritual nature and one's relationship to self, family, groups, Mankind, all life forms, the material universe, the spiritual universe and the Supreme Being."
What are the origins of scientology?
It claims to have roots in the beliefs of "all great religions" and thus encompasses "a religious heritage as old and as varied as Man himself" so could be seen as 50,000 years old.
What are the actual origins?
It was founded by a man named Lafayette Ron Hubbard - known as L. Ron Hubbard - from New Jersey, US, who wrote a book on "dianetics" in 1950. Four fans, described as an attorney, a publisher, a doctor and an engineer, then formed the Hubbard Dianetics Research Foundation.
The first Church of Scientology was established in February 1954, and more than a dozen churches sprang up over the next decade.
Hubbard, a former science fiction writer, died in 1986. His former assistant,David Miscavige, 56, has been leader of the church since.
What is the basis of their beliefs?
Scientology begins with the concept that man is "basically good, and that his spiritual salvation depends upon himself, his fellows and his attainment of brotherhood with the universe."
The fundamental principles are threefold:
• Man is an immortal spiritual being;
• His experience extends well beyond a single lifetime;
• His capabilities are unlimited, even if not presently realised.
What is the appeal of scientology?
According to the church, people believe in scientology because of an "absence of answers" from science.
They claim scientology supplies "workable methods of application, that made it possible for Man to reach the ancient goal he has been striving toward for thousands of years: to know himself and, in knowing himself, to know and understand other people and, ultimately, life itself".
Scientology means "knowing how to know". It is a contraction of the Latin word scio ("knowing, in the fullest sense of the word") and the Greek logos ("study of").
Where is it based?
In a 202ha compound about 160km from Los Angeles, known as the "Gold Base". The desert site was bought by the church in 1978 and at least $51 million has been spent redeveloping it.
It also has a 24ha UK base - the former home of Hubbard - called Saint Hill Manor, in Sussex. It's also now the home of Hollywood megastar and scientology devotee Tom Cruise, according to reports.
Do they celebrate any holidays?
Yes. Hubbard's birthday in March, the anniversary of the first publication of Dianetics in May, and Auditor's Day in September.
How do they deal with pain?
They believe the spirit can alleviate "injury, trauma or discomfort" by "putting the spirit in communication with the body". The church advises a method of detoxification involving saunas, exercise, vitamins, the drinking of oils, as well as light jogging.
They believe life is compartmentalised into eight "dynamics". The First Dynamic, experienced by babies, is explained as an "urge towards existence" and the Eighth is an "urge toward infinity".
They call a spiritual being "Thetan", meaning "the source of all life or life itself".
Do they believe in God?
They have a concept of God or a Supreme Being, but no set dogma. They explain: "Scientologists take the maxim quite to heart that God helps those who help themselves."
Do they believe in reincarnation?
They believe in "past lives", and a person being born again.
A person cannot progress unless "aberrations" from past lives are dealt with. The concept of heaven or hell therefore relates to a future life, with experiences being earned by behaviour.
"In other words, the individual comes back," they say. "He has a responsibility for what goes on today since he will experience it tomorrow."
Do they believe in charity?
Tentatively, and with caveats. They explain: "Some form of exchange is necessary in any relationship. If a person only receives and never gives, he will lose his own self-respect and become an unhappy person."
How do they raise children?
Scientologists believe children are spiritual beings occupying young bodies, and should be given the same respect as adults.
Can they cure drug addicts?
They claim so. They have established rehabilitation centres in more than 40 countries practising "narconon", meaning "no drugs".
Can they help criminals?
They run a programme called "criminon", or "no crime".
What is their relationship with the media?
They say: "In recent years, church representatives have met with the editorial boards of major media outlets to brief them on Scientology, its policies and its activities. These meetings help dispel the rumors and false allegations that have gathered in reference files over the years.
"Such meetings have been very beneficial for both the Church and journalists."
The media says: "Very weird cult ... Something creepy, maybe even evil, about these people." - Rupert Murdoch
It has been reported that scientologist believe in xenu, an extraterrestrial dictator who brought billions of people to Earth in a spacecraft 75 million years ago.
The essence of these people remains, causing spiritual harm to those in the modern day, it is claimed.
An official statement from the church, however, says: "Absolutely not. Scientology holds no such belief. Any suggestion otherwise is as absurd as asserting that those of the Christian faith believe themselves descended from aliens because they believe there is a Heaven."
How is it funded?
Through donations from members. The church explains: "Scientology does not have hundreds of years of accumulated wealth and property like other religions; it must make its way in the world according to the economics of today's society."
Are there any famous scientologists?
Yes - many. Tom Cruise is probably the most famous. John Travolta, Kirstie Alley and Lisa Marie Presley have all been said to believe in scientology.
Has it been involved in any controversy?
Yes, a lot.
Among the numerous court cases, reports and rumours involving scientology are allegations of human trafficking, holding people against their will and members cutting ties from their families.
The church says: "Like all new ideas, Scientology has come under attack by the uninformed and vested interests. The so-called controversy of Scientology is merely the bitter old resisting the ambitious new."
The Church has its own cruise ship, the MV Freewinds, based in Curacao, for the most committed members. A former member claims she was held against her will on board for 12 years and forced to perform hard labour.
An Australian senator called Scientology a "criminal organisation" and accused it of embezzlement and blackmail.
Does it require any commitment?
The official scientology website says members sign a "a one-billion-year pledge to symbolise their eternal commitment to the religion."
Where can I learn more about scientology?
There are more than 15,000 pages of technical writing and more than 3000 taped lectures on scientology.
The church claims: "Its truths are self-evident, its principles are easily demonstrable and its technology can be seen at work in any Church of Scientology."
Five Scientology scandals
David Miscavige's father, Ron, publishes Ruthless in May 2016, detailing his relationship with the Scientology leader. The church accuses Ron of trying to make money from his surname, saying "any father exploiting his son in this manner is a sad exercise in betrayal".
2 Going Clear
A highly-critical documentary, Going Clear: Scientology and the prison of belief, airs on US television network HBO in March 2015. Those interviewed are dismissed by the Church as "a collection of deadbeats, admitted liars, self-admitted perjurers, wife beaters and worse".
3 Leah Remini
Remini, an American actress, publishes her memoir Troublemaker: Surviving Hollywood and Scientology in November 2015. She accuses Miscavige of being controlling and oppressive. The Church says she is simply regurgitating discredited myths, and describes her as pathetic, bitter and angry.
4 The Apostate
Oscar-winning film director and producer Paul Haggis is interviewed for a 25,000 word article in The New Yorker in February 2011, in which he describes his 35-year membership of "a cult". The Church brought 47 volumes of research material to an all-day meeting with the author, editor and fact-checker but has never taken legal action against the explosive article.
5 Tom Cruise
Tom Cruise, who was introduced to Scientology in the late 1980s by his ex wife, Mimi Rogers, is interviewed on US breakfast chat show Today. Cruise, believed to be second in command only to Miscavige, gets into a furious argument in June 2005 with host Matt Lauer about prescription drugs. He has since refused to discuss his religion.
March 13, 1911
Lafayette Ronald Hubbard, known as L. Ron Hubbard, born in Nevada.
Hubbard, now a successful science fiction writer, publishes his first article explaining his theory of how the mind works, which he called dianetics.
Hubbard announces the creation of the Church of Scientology - describing Scientology as a religion focused on the spirit. He defined dianetics as a science that addressed the physical being.
1960s and 70s
Hubbard sets sail with his followers to travel the world and live at sea. He styles himself as the Commodore, and his devotees are known as the Sea Org. They sail until a slew of countries, including the UK, close ports to him.
Hubbard returns to the USA and spends much of the rest of his life in seclusion in the California desert.
David Miscavige, who was introduced to Scientology by his father as a way of treating his asthma, drops out of high school and moves to Florida to serve the organisation.
Miscavige is put in charge of the unit that deals with legal issues relating to Scientology. He gains in influence, taking control of financial affairs and reorganising the management hierarchy.
January 24, 1986
Hubbard dies and Miscavige takes over. He expands the organisation from his base in Hemet, California, and a massive centre in Clearwater, Florida.
Miscavige gives his first newspaper interview, to the St Petersburg Times, in Florida. After six hours of interviews he is described as being the Scientology equivalent of the Pope.
Miscavige's brother, Ron, leaves the organisation. His father, also Ron, and two sisters, Denise and Lori, remain in the church.
Tom Cruise, interviewed on USA breakfast chat show Today, gets into a furious argument with the host Matt Lauer about prescription drugs.
Miscavige is best man at Tom Cruise's wedding to Katie Holmes.
British journalist John Sweeney makes a documentary for Panorama, Scientology and Me, in which he famously engaged in a shouting row with Scientology representative Tommy Davis. He produced a follow-up three years later.
The last time Miscavige's wife Shelly, a fellow Scientologist, is seen in public. The Church says she is simply doing work for the church away from the public eye.
Tom Cruise is presented with a medal for his services to Scientology, and praises Miscavige as the most "intelligent, tolerant, compassionate being" he has met - adding: "and I have met the leaders of leaders."
The St Petersburg Times publishes a series of articles entitled "The Truth Rundown", in which a group of high-ranking former Scientologists make damning accusations of tyranny and physical violence.
Jenna Miscavige Hill, David's niece, publishes a book about her experience of Scientology. She describes the church as "evil". The church calls it a "ludicrous" book of "tabloid tales".
Louis Theroux's documentary,
, premieres at the Tribeca film festival.