Psionics means the pseudoscience of psychic abilities. The evidence for psychic abilities is disputed, and their existence is controversial, as there has been no reproducible scientific confirmation of any such effects; only sparse anecdotal evidence from mostly conflicted sources.

However, believers in psychic phenomena have developed numerous hypotheses about their function. Beliefs on how these alleged abilities work vary greatly.

The term, psionics, is also a recurring element in fiction, usually works of fantasy and science fiction as well as video games, especially role-playing games.

B. P. Wiesner and Robert H. Thouless first proposed the term "psi" in 1942 as a more general term to include both extrasensory perception and psychokinesis. The original terminology proposal divided psi into psi-gamma, for cases of perception, and psi-kappa, for cases of action. These terms were later modified into "passive psi" and "active psi"

In the 1970s the United States and the Soviet Union engaged in an exploration of the potential military value of a particular psionic ability: that of visualizing a location without physical travel or "remote viewing". In the United States, this project, begun at the behest of the CIA at the Stanford Research Institute, became widespread public knowledge in the mid 1980s and was terminated based on concerns about effectiveness in 1995. This project is known as the 'Stargate' program. Many are skepticle about the actuallity that that the 'Stargate' program ever existed.

The "psi" catalyst, as with many paranormal forces, is often referred to generally as an "energy" whose physical properties are generally thought to be difficult or impossible to measure in terms of standard physics. Psionic energy can also be compared to many eastern forms of bioenergy including the Qi in Qigong or prana in Indian meditation.

Although some claim that any energy that can be manipulated solely by the mind is considered psi, others contend that there are distinctions that can be made between energy forms. Common distinctions are between 'life energy', 'earth energy', and psi energy. Those who make these distinctions usually do so on the basis that the different energies have a different 'feel' to them, and thus can be separated. Common ways energy can be manipulated is by generation, changing direction or velocity, density, and shape. This is done through intention coupled with intense focus usually also including the use of visualization for beginners. Additional suggested mechanisms for manipulation of such energies include connections with the subconscious mind, and special breathing techniques.

Psionics are usually claimed to be strictly mental abilities which do not include any magick or rituals. The main source of power is from the mind, and many supposed practioners draw a distinction between psychic abilities and spirituality. However, there are also those who believe that psychic and spiritual or mystical abilities are related, or even indistinguishable, including some who claim to be psychics. Because of the subjective nature of these experiences, and the lack of measurable proof, the lines between psionics and mysticism are not clear.

According to some psionic practices, constructs are masses of dense psionic energy that have been formed into a specific shape and given a specific task to perform. This can range from a simple shield (a shield being a construct that regulates or stops the energy passing through it), on up to creating artificial "entities", or constructs with programmed sentience. A common example that many beginning psions start out with is a 'psiball', which is essentially a simple construct programmed to retain a spherical shape.