Mentalism is a performing art in which its practitioners, known as mentalists, appear to demonstrate highly developed mental or intuitive abilities. Mentalists perform a theatrical act that includes special effects that may appear to employ psychic or supernatural forces but that is actually achieved by "ordinary conjuring means", natural human abilities (i.e. reading body language, refined intuition, subliminal communication, emotional intelligence), and an in-depth understanding of key principles from human psychology or other behavioral sciences. Performances may appear to include hypnosis, telepathy, clairvoyance, divination, precognition, psychokinesis, mediumship, mind control, memory feats, deduction, and rapid mathematics.

Mentalism is commonly classified as a subcategory of magic and, when performed by a stage magician, may also be referred to as mental magic. However, many professional mentalists today may generally distinguish themselves from magicians, insisting that their art form leverages a distinct skillset. Instead of doing "magic tricks", mentalists argue that they produce psychological experiences for the mind and imagination, and expand reality with explorations of psychology, suggestion, and influence. Mentalists are also often considered psychic entertainers, although that category also contains non-mentalist performers such as psychic readers and bizarrists.

Notable magicians Penn & Teller and James Randi argue that a key difference between a mentalist and a psychic is that the former is a skilled artist or entertainer who accomplishes their feats through practice, while the latter conventionally claims to have supernatural experiences and/or receive divine revelations from God.

Renowned mentalist Joseph Dunninger, who also worked to debunk fraudulent mediums, captured this key sentiment and described his abilities in the following way: "Any child of ten could do this – with forty years of experience." Like any performing art, mentalism requires years of dedication, extensive study, practice, and skill to perform well.

Much of what modern mentalists perform in their acts can be traced back directly to "tests" of supernatural power that were carried out by mediums, spiritualists, and psychics in the 19th century. However, the history of mentalism goes back even further. Accounts of seers and oracles can be found in the Old Testament of the Bible and in works about ancient Greece. Paracelsus reiterated the theme, so reminiscent of the ancient Greeks, that three principias were incorporated into humanity: the spiritual, the physical, and mentalistic phenomena. The mentalist act generally cited as one of the earliest on record in the modern era was performed by diplomat and pioneering sleight-of-hand magician Girolamo Scotto in 1572. The performance of mentalism may utilize conjuring principles including sleights, feints, misdirection, and other skills of street or stage magic. Nonetheless, modern mentalists also now increasingly incorporate insights from human psychology and behavioral sciences to produce unexplainable experiences and effects for their audiences. Changing with the times, some mentalists incorporate a smartphone into their routine.

Mentalists typically seek to explain their effects as manifestations of psychology, hypnosis, an ability to influence by subtle verbal cues, an acute sensitivity to body language, etc. These are all genuine phenomena, but they are not sufficiently reliable or impressive to form the basis of a mentalism performance. These are in fact fake explanations - part of the mentalist's misdirection - masking the use of classic magicians' trickery.

Often one of the key ways a mentalist will accomplish giving the impression of "mind reading" will be through gaining the relevant "thought" through other, physical means. Information about a participant's thought might be made available through written pieces of paper, envelopes, books, or playing cards that can then be obtained through the use of sleight of hand. Modern technology has also allowed for the creation of various apparatus enabling the gathering of such information electronically from a distance. At times these techniques and tools have also allowed mentalists to "predict" thoughts through creating "proof" of the prediction after the thought itself has been revealed.

This technique involves implanting an idea, thought, or impression in the mind of the spectator or participant. The mentalist does this by using subtle verbal cues, gestures, body language, and sometimes visual aids to influence their thoughts. For instance, asking someone to "think of any card in a normal deck" automatically plants the general idea of a playing card in their mind. Similarly, asking them to "visualize the card clearly in your mind" can put the image of a particular card in their imagination.