Dianetics is the name given to a set of principles designed to explain the functioning of the human mind, and as a system for curing some forms of mental illness. Devised by L. Ron Hubbard, writer of western fiction, romance novels, screenplays, mystery, fantasy and science fiction, it was first publicized by a series of articles in Astounding Science Fiction. Later the principles were consolidated in the book Dianetics: The Modern Science of Mental Health, first published in 1950. The principles of Dianetics constitute the primary dogma of Scientology.
Dianetics presents itself as a systemic method of identifying the causes of and relieving many of an individual's mental, emotional or (psychosomatically) physical problems. Fundamental to the system is the concept of the engram, which is defined as "a definite and permanent trace left by a stimulus on the protoplasm of a tissue.". Engrams are created during periods of psychological distress or trauma, and are at the root of all mental disorders.
Dianetics is often regarded as a pseudoscience, as it presents itself as a "scientific" system of knowledge, yet fails to meet the requirements of the scientific method. Hubbard in Dianetics' states: "[Dianetics is]...an organized science of thought built on definite axioms: statements of natural laws on the order of those of the physical sciences" . Critics would argue that a 'definite axiom' is an oxymoron, and regardless, a science cannot be based on axioms, only on hypotheses based on experimental evidence.
Regardless of its scientific status, Dianetics may legitimately be regarded as an interpretive or philosophical system of knowledge, and on this basis the book Dianetics is considered by some as the "bible" of Scientology.
See also: http://www.skepdic.com/dianetic.html