The upper levels of Scientology

Scientologists who have achieved the State of Clear may continue onto the Upper or OT (Operating Thetan) Levels. These courses are available by Church invitation only after a review of the candidate's character, ethics and contribution to the Aims of Scientology.[26] The contents of these advanced courses are held in strict confidence within the Church and individuals who have read these materials may neither discuss nor disclose what they contain without jeopardizing their standing in the Church.[citation needed] Presently, there are eight such levels, OT I to VIII. Church management has promised to release a ninth OT level once certain expansion goals are met.[27] The highest level released to date, OT VIII, is only granted at sea, on the Scientology ship, the Freewinds, which was established to provide a "safe, aesthetic, distraction-free environment" where this OT level could be delivered.[28]

Source: http://en.wikipedia.org/wiki/Scientology