This is a list of speculative, fringe or disputed theories. This includes examples of fields of endeavor that many consider to varying extents to be pseudoscientific. Pseudoscientific practices are often quite popular, in part because they often work, possibly due to the placebo effect or observer bias. Many pseudosciences are associated with the New Age movement and there is a tendency to improperly associate all practices of the "New Age" with pseudoscience.

Inclusion in the list is possible because a theory is:

1. Asserting claims without supporting experimental evidence;
2. Asserting claims which contradict experimentally established results;
3. Failing to provide an experimental possibility of reproducible results; or
4. Violating Occam's Razor (the principle of choosing the simplest explanation when multiple viable explanations are possible).
5. Adhered to by a limited group.

• Acupuncture is the practice of inserting very thin needles in particular points on the body to improve health and well-being, and is one component of traditional Chinese medicine.
• Anthropogenic global warming theory attributes some portion of global warming and other climate changes to human activity, including but not limited to the introduction of greenhouse gases into the atmosphere.
• Applied kinesiology is a method of diagnosing malfunctioning organs and what the effect of substances on the body is or would be by testing whether certain muscles is weakened or not.
• Astrology refers to any of several systems of understanding, interpreting and organizing knowledge about reality and human existence, based on the relative positions and movement of various real and construed celestial bodies.
• Biorhythm theory researches patterns of alterations in physiology, emotions, and intellect.
• Cartomancy is a form of fortune telling -- divination -- using a deck of cards.
• The Catastrophism theory is that Earth has been affected by sudden, short-lived, violent events that were sometimes worldwide in scope
• Channeling supposed special ability of a person to receive information from an unknown sources.
• Characterology method of character reading developed in the 1920's.
• Some Chiropractic theories that ascribe ailments unrelated to the spine to spinal maladjustments.
• Chiromancy evaluates a person's character or future life by "reading" the palm of that person's hand.
• The Cold fusion (or cold nuclear fusion (CNF)) theory claims that hydrogen can undergo nuclear fusion at room temperature in palladium.
• Creationism is the belief that the origin of the universe and everything in it is due to an event of creation brought about by the deliberate act of a creator god.
• Cryptozoology is the study of rumored or mythological animals that are presumed by many to exist, but for which proof does not yet exist.
• Crystal power theory states that crystals have alleged healing and mystical paranormal powers.
• Dowsing divination method which dowsers say empowers them to find water, metals and hidden objects by carrying some form of stick and watching its motion.
• The Duesberg hypothesis states that the HIV virus does not cause AIDS.
• Nikola Tesla's Dynamic theory of gravity that was never published but has been modified.
• Engrams are neurons patterns connected through activation at the same time.
• Facilitated communication is alternative means of expression for people who cannot speak, or whose speech is highly limited (e.g. echoed, limited to one or a few word utterances), and who cannot point reliably.
• Food faddism refer to the tendency for idiosyncratic diets and eating patterns.
• Fortune telling is the practice of predicting the future, usually of an individual, through mystical or supernatural means.
• Sigmund Freud's Freudian theory which is a core element of psychoanalysis.
• Geomancy has always been a method of divination that interprets markings on the ground or how handfuls of dirt land when you toss them.
• Graphology is the study of handwriting and its connection to behavior, personal information and other human traits.
• Hidden variable theory is urged by a minority of physicists who argue that the statistical nature of quantum mechanics implies that it is really applicable only to ensembles of particles.
• The Hollow Earth theory claims that the Earth is hollow, and is possibly populated by a race of superbeings, humans or aliens, and possibly dinosaurs.
• Homeopathy is a system of alternative medicine involving the use of highly diluted substances with similar (i. e. homeo-) characteristics to the condition being treated.
• Hydrino theory proposes the hydrino, or miniature hydrogen atom with the electron pushed closer than usual to the nucleus.
• Hypnosis is "a procedure during which a health professional or researcher suggests that a client, patient, or subject experience changes in sensations, perceptions, thoughts, or behavior."
• Intelligent Design theory holds that life and living things show signs of having been designed. ID's primary argument is that life is too complex to have simply "happened."
• Interpretation of dreams is the art of determining the meaning (or alleged meaning) of the symbols contained in a dream.
• Iridology theory that diagnoses the health of a person by examining the pattern of the Iris of the eye.
• Kirlian photography is high-voltage contact print photography.
• Ley lines are alignments of a number of places of geographical interest, such as ancient megaliths.
• Luminiferous aether is the classical medium for the propagation of light.
• Magnet therapy is an alternative medicine based on the concept that certain medical disorders can be effectively treated by exposure to magnetic fields.
• Marxism-Leninism a utopian political and economic theory based on economic determinism.
• Numerology is an arcane study of the purported mystical relationship between numbers and the character or action of physical objects and living things.
• Wilhelm Reich's Orgone energy is an unproven form of energy.
• Parapsychology is the branch of science concerned with the study of mental phenomena, whether actual or purported, that are not currently explainable within the framework of mainstream, conventional science.
• Perpetual motion machines are a class of hypothetical machines which produce useful energy "from nowhere".
• Pathognomy is the study of passions and emotions.
• Photoreading is "mentally photographing" printed pages.
• Phrenology claims to be able to determine personality traits and criminality on the basis of the shape of the head.
• Physiognomy is based upon the belief that the study and judgement of a person's outer appearance, primarily the face, reflects the contents of their personality.
• Plasma cosmology is a sub-set of plasma physics which attempts to explain large scale structure in the universe.
• Polygraph is a device which measures and records several physiological variables such as blood pressure, heart rate, respiration and skin conductivity while a series of questions is being asked, in an attempt to detect lies.
• Pseudoarchaeology refers to the ideologically-driven, usually sensational interpretation of the past outside of a critical, scientific framework. Pseudoarchaeology also includes forms of protosciences.
• Psychic surgery is a type of apparent surgery performed by the healer with bare hands or unorthodox instruments.
• Pyramid power theory states that pyramids have healing power and spiritual energy.
• Racially prejudiced psychometrics, as in The Bell Curve by Herrnstein and Murray
• Quaternion physics is a method to represents events as time (t) and place (x, y, z).
• Reciprocal System of Theory postulates a universe of nothing but motion.
• Recovered memory is the act of discovering repressed memories and therapy to achieve such ends.
• Remote viewing is a form of clairvoyance by which a viewer is said to use his or her clairvoyant abilities to "view" which is hidden from physical view of the viewer.
• Scrying is the name given to the ancient technique of gazing into an object.
• Social Darwinism is a set of theories which proponents argue govern the natural sociological relations of humanity; these theories are derived from Darwin's theory of evolution.
• The Steady state theory holds that the universe has always existed, and always will exist.
• Superficial anatomy researches forms and proportions of the human body and the surface landmarks which correspond to deeper structures hidden from view.
• Gene Ray's Time Cube. It is doubtful whether this concept even qualifies as a theory as it does not provide any testable constructs and Gene Ray refutes the scientific method itself.
• Ufology is the term describing the study of the UFO (unidentified flying object) phenomena, including claims that some UFOs are extraterrestrial vehicles manned by aliens.