The Church of Scientology is a cult/religion created by science fiction author L. Ron Hubbard in the 1950s. It is a proselytic organization, drawing in new members through free personality tests. Scientology is secretive group: most members are not aware of the entire dogma or practices of the organization. To progress within Scientology and become initiated into the core theology, expensive fees must be paid. When revealed, the core beliefs of Scientology read like a bad science fiction novel.
The group is notorious for using legal threats and action to intimidate and silence its opponents, especially those who try to convince Scientologists to leave the organization, those who attempt to demonstrate the cult-like nature of the organization, and those who expose Scientology secrets that are supposed to be reserved for senior-level Scientologists. Scientologists are required to shun family members and friends who do not approve of Scientology.
"I’d like to start a religion. That’s where the money is."
- — L. Ron Hubbard to Lloyd A. Eshbach, in 1949 
Based on their absurd beliefs and statements of their founder and members, Scientology is nothing more than a grandiose money-making scam invented by an unscrupulous charlatan with no regard for the psychological well-being of others. The Church is extremely wealthy and draws attention from the fact that several prominent celebrities are members. The Church is avidly opposed to the fields of psychiatry and psychology.
Scientology is an unusual religion in that its dogma is not outwardly publicized by the group. This is similar to the mystery cults of the ancient Greek world. However, ex-members have leaked documentation that describes their core theology and practices. Scientology is extremely fond of jargon, with a whole galaxy of terminology for various real and imaginary concepts. 
Auditing, E-meter, Security Checks
Scientologists often prosthelytize using a "personality test" or a "free stress test". No matter how one scores on Scientology's personality test, the tester informs the inductee that that there is something wrong with their personality that Scientology can help with. This leads to a process called "auditing", involving a device called an E-meter. The E-meter is a device with two handles that measures the electrical resistance in the human body. The E-Meter is a variation of a Wheatstone Bridge, which determines resistance of an unknown component, in this case, the skin of the subject. Due to galvanic skin response, the resistance of skin can vary significantly in conjunction with the state of mind of the subject.  According to Scientology doctrine, this device measures "thetans", which are distraught souls inhabiting our body.
The e-meter is primarily used as a tool for "auditing", however, it is also used as a makeshift lie detector during "Security Checks", which are semi-annual interrogations used to discover criminal and subversive behavior in people as young as 6 years. The church may use information derived from these checks to blackmail individuals who become critical of the cult. The church has methods of interrogating even uncooperative subjects. By strapping the e-meter's electrodes to the soles of the feet, or into the armpits of the subject and asking questions, the interrogator can attempt to determine answers even if the subject refuses to speak. However, attempting to detect a lie using this or any other current technology is mere pseudoscience.  The E-meter is more effective as a tool of intimidation and deception, rather than being an effective lie detector.
Thetans and Xenu
Scientology has various stages that members pass through, which get progressively more expensive as the Scientologist is compelled to purchase more and more materials and books related to the doctrine. After spending about $360,000, the Scientologist reaches stage OT III, where the story behind the thetans is revealed.
It begins 75 million years ago with a galactic dictator named Xenu, who had a problem with overpopulation on many of the planets he ruled over. He tricked billions of aliens into being frozen and loaded onto rocket ships which were exactly like DC-8 airliners except with rocket engines. The rocket ships were sent to Earth, then called "Teegeeack", and the aliens were placed next to several specifically named volcanoes (most of which were not even in existence 75 million years ago, unbeknownst to geologists of Hubbard's time), and exploded with hydrogen bombs. The souls of the dead aliens are said to have roamed the Earth until they could find human bodies to attach to. Scientologists proclaim that thetans occupying our bodies are the source of all our mental problems, and that Scientology is the only way to get rid of the thetans.
Of course, there is no evidence that any of this is true apart from the say so of L. Ron Hubbard.
Fair game is (or was) a Scientology practice that allows for any and all methods to be employed against the church's enemies. It was instituted in 1950s, supposedly cancelled in 1968 but mentioned in internal documents until at least 1980. Perhaps because of this policy, critics of the church are often objected to intimidation, harassment, character assassination and other legal or illegal measures. 
- "Fair game. May be deprived of property or injured by any means by any Scientologist without any discipline of the Scientologist. May be tricked, sued or lied to or destroyed. "
The church denies "fair game" was a mandate for illegal punishment. Some have claimed that other policies are more significant in explaining the churches actions, such as "The Responsibilities of Leaders".  Harassment of critics by the church continues to this day and is referred to as fair game by the church's critics.
- ↑ L. Ron Hubbard to Lloyd A. Eshbach, in 1949; quoted by Eshbach in OVER MY SHOULDER: REFLECTIONS ON A SCIENCE FICTION ERA, Donald M. Grant Publisher. ISBN 1-880418-11-8, 1983
- ↑ Glossary of the Scientology Critical Information Directory
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- Official website of the Church of Scientology
- Chruch of Scientology Profile on the Virginia Commonwealth University World Religions and Spirituality Project
- Controversies And Misconceptions About Scientology
- The Young Turks, What Really Happens In The Church of Scientology, 31 Mar 2015
- Operation Clambake: The Inner Secrets Of Scientology
- Rick A. Ross Institute's Scientology page
- Scientology Kills
- Scientoligeist - The Curse of Xenu a humorous play about ghosts and other paranormal stuff that draws readers' attention to problems with Scientology while entertaining them.
- The Way of Reason - The Truth About Scientology
- Dogma Free America - Interview with Valerie Emanuel of scientology-kills.org