Parapsychology is the scientific study of the evidence of mental awareness or influence of external objects without interaction from known physical means. Most objects of study fall within the realm of "mind-to-mind" influence (such as extra-sensory perception, folie a deux and telepathy), "mind-to-environment" influence (such as psychokinesis) and "environment-to-mind" (such as hauntings). Collectively, these abilities are often referred to as "psionics".

The scientific validity of parapsychology research is a matter of frequent dispute and criticism, and is generally referred to as a pseudoscience, refuted by numerous rigorous scientific studies. Nonetheless, many eminent scientists have been firm believers that the field is worthy of analysis, such as Wolfgang Pauli (See Pauli Effect).

The phenomena in question fall into two broad groups.

Extra-sensory perception (ESP) is also known as anomalous cognition, and includes telepathy, clairvoyance, clairaudience, clairalience, clairgustance, clairsentience, precognition, postcognition, psychometry, and dream transference.

Anomalous operation includes psychokinesis (in the past referred to as telekinesis), pyrokinesis, psychogenesis, out-of-body experiences, astral projection, near-death experiences, mediumship, and reincarnation.

The general term "psi phenomena" (or the somewhat older term, "psychic phenomena," which was said to be the "psi factor" in an experiment) covers all of these categories.

The standing of the field of parapsychology has always been controversial within the scientific community.

As its name indicates, parapsychology is sometimes considered a sub-branch of psychology, and this has arisen historically since it involved the study of apparent mental faculties. In its modern form, parapsychology is an interdisciplinary field, which has attracted physicists, engineers, and biologists, as well as psychologists and those from other sciences. (For an argument that parapsychological phenomena may not in fact be psychological, see Peter J. King's "Parapsychology without the 'Para' (or the 'Psychology')" (Think 3, 2003, pp 43 53).)

Parapsychology often involves the use of new and untested technologies and methods such as neurofeedback, Neuro-linguistic programming, past life regression and so on.

Many people are not satisfied with the term, and have proposed alternatives, such as "psi research" (similar to the older term "psychical research"), but "parapsychology" is the term that has gained the greatest acceptance today.

One organization involved in the field, the Parapsychological Association is an affiliate of the American Association for the Advancement of Science (AAAS).  At present (2006) there are about two hundred and seventy five members in the Parapsychological Association.

In the scientific disciplines, there is a belief that all claims should be treated with scientific skepticism. Mainstream scientists generally argue that after examining psi claims for over a century, there has been significant difficulty assertaining significant positive evidence for such claims.

Many in the scientific community believe that parapsychology is not a real science, that psi phenomena do not exist, and that parapsychology is a pseudoscience. Many scientists and skeptical observers of the field believe that some parapsychologists knowingly commit fraud; that some are incompetent or misled by their own hopes or desires; and that some are naïve and therefore easily deceived by fraudulent participants; or perhaps some combination of the above. One of the most famous cases in psychology that illustrates being misled by one's hopes is that of Clever Hans. Mr. Wilhelm von Osten, who promoted the horse, did not intend to defraud anyone, but he fooled himself and large audiences nevertheless.

Parapsychologists disagree with this assessment. Many have been formally trained in science, and are familiar with the scientific method. Statistician Jessica Utts has shown in a number of papers that:
"Using the standards applied to any other area of science, it is concluded that psychic functioning has been well established. The statistical results of the studies examined are far beyond what is expected by chance. Arguments that these results could be due to methodological flaws in the experiments are soundly refuted."

The precise percentage of scientists holding negative views about parapsychology is unclear, since surveys targeting this group are far less common than those targeting the general population. In his article Save Our Science: Paranormal Phenomena and Zetetics, skeptic Henri Broch complains:
"These data are based on an investigation on the belief in parasciences among Frenchmen (published in 1986). [...] Contrary to what might have been thought, the level of belief in the paranormal is directly proportional to the level of education, whatever the religious persuasion may be. Those with higher scientific degrees fare slightly better, although their level of belief is superior to [greater than] the average!"

Some skeptics believe that there is a tendency for parapsychology researchers to select "good days" and discard "bad days" for the people in the test samples. But the "Theory of Runs" shows that the chance of a long run of successes (or failures) increases drastically when the periods of success or failure are selected as part of a larger sample. See: Feller, William (1968), An Introduction to Probability Theory and Its Applications, vol. I, John Wiley & Sons, New York, NY, p. 86. For a more recent discussion of the theory and the "arcsine law" .

Andrew Greeley, a Catholic priest and a sociologist from the University of Arizona, studied surveys on belief in ESP from 1978 through 1987, and studied the mental health of believers in ESP. The surveys he studied showed that from 1978 through 1987, the number of American adults who reported psychic experiences rose from 58% to 67% (clairvoyance and contacts with the dead were reported by 25% of his respondents). According to Greeley, the elderly, women, widows and widowers, and the conventionally religious report higher incidents of such experiences. He also tested the psychological well-being of people reporting mystical experiences with the "Affect Balance Scale" and found that people reporting mystical experiences received top scores. Greeley summarized his findings by writing,

A few parapsychologists are skeptics, for example Chris French and his colleagues at the Anomalistic Psychology Research Unit at Goldsmiths College in London, and Richard Wiseman and his colleagues at the Perrott-Warrick Research Unit in the Psychology Department of the University of Hertfordshire, both of which units include individuals who are members of the Parapsychological Association. These researchers do not approach the field with a belief in the paranormal, but are rather interested in the purely psychological aspects of those who report paranormal experiences, along with the study of the psychology of deception, hallucination, etc. These researchers also have provided their own guidelines and input to other parapsychologists for the design of experiments and how to properly test those who claim psychic abilities. While some of these guidelines have been useful, many have suffered from a naive understanding of scientific practice in general and in parapsychology in particular, from a distorted view of the methodology actually in use in the field, and the unfortunate habit of some skeptics to make sweeping statements about the applicability of counter-hypotheses to lines of research without actually investigating the appropriateness of those counter-hypotheses to the details at hand. (See, for example a mostly-positive review of one of these guidelines written by skeptics)

The most important point that both proponents and skeptics raise is the need to be critical of the theory, methods, and conclusions of any one who investigates or comments on parapsychology as a science, no matter what point of view they represent. In order to be an objective professional, one must have a first-hand knowledge of the vast past and present published scientific literature in the field, primary and scholarly sources of its age whenever possible, and -- even more important -- have first-hand experience as an experimenter or investigator and a respect for the art of conjuring and its masters. The hands-on approach is essential to scientific progress in the field, whether one approaches it from a "paranormalist" or a "conventional theorist" point of view. Selective and historically uninformed armchair cheerleading and armchair skepticism are equally useless in all fields of inquiry and science.

Many scientists hold that the entire body of evidence to date is of poor quality and not properly controlled; in their view, the entire field of parapsychology has produced no results whatsoever. Frequently, however, proponents argue that those who hold this view have not had any contact with the published literature of the field such as that which can be found in the Journal of Parapsychology, the Journal of the Society for Psychical Research, the Journal of the American Society for Psychical Research, or in the proceedings of the annual convention of the Parapsychological Association[citation needed]. Instead, they have relied on the analyses made by members of the skeptical community who, wrongly, assume that all parapsychological experiments suffer from flaws and therefore no parapsychological experiment may be considered evidential even in the weak sense of the term. Working psi researchers welcome criticisms that are based on knowledge of the peer-reviewed, published literature of the field. Criticism and blanket statements based on hearsay are not productive and not encouraged in any area of science.

Other scientists hold that there is a small amount of data from properly controlled experiments that can be trusted for a small number of psi phenomena. They hold that this evidence is not definitive, but suggestive enough to warrant further research.

Other scientists, who are familiar with the published literature of the field of parapsychology, believe that a great deal of evidence has been collected, which, if it addressed more conventional phenomena, would be sufficient to provide proof.