Psychological projection is a defence mechanism in which the human ego defends itself against unconscious impulses or qualities (both positive and negative) by denying their existence in themselves while attributing them to others. For example, a bully may project their own feelings of vulnerability onto the target. It incorporates blame shifting and can manifest as shame dumping.
A prominent precursor in the formulation of the projection principle was Giambattista Vico. In 1841, Ludwig Feuerbach was the first enlightenment thinker to employ this concept as the basis for a systematic critique of religion. The Babylonian Talmud (500 AD) notes the human tendency toward projection and warns against it: "Do not taunt your neighbour with the blemish you yourself have." In the New Testament, Jesus also warned against projection: "Why do you look at the speck of sawdust in your brother's eye and pay no attention to the plank in your own eye? How can you say to your brother, 'Let me take the speck out of your eye,' when all the time there is a plank in your own eye? You hypocrite, first take the plank out of your own eye, and then you will see clearly to remove the speck from your brother's eye." 
Projection (German: Projektion) was conceptualised by Sigmund Freud in his letters to Wilhelm Fliess, and further refined by Karl Abraham and Anna Freud. Freud considered that, in projection, thoughts, motivations, desires, and feelings that cannot be accepted as one's own are dealt with by being placed in the outside world and attributed to someone else. What the ego repudiates is split off and placed in another.
Freud would later come to believe that projection did not take place arbitrarily, but rather seized on and exaggerated an element that already existed on a small scale in the other person. (The related defence of projective identification differs from projection in that there the other person is expected to become identified with the impulse or desire projected outside, so that the self maintains a connection with what is projected, in contrast to the total repudiation of projection proper.)
Melanie Klein saw the projection of good parts of the self as leading potentially to over-idealisation of the object. Equally, it may be one's conscience that is projected, in an attempt to escape its control: a more benign version of this allows one to come to terms with outside authority.
Projection tends to come to the fore in normal people at times of personal or political crisis but is more commonly found in personalities functioning at a primitive level as in narcissistic personality disorder or borderline personality disorder.
Carl Jung considered that the unacceptable parts of the personality represented by the Shadow archetype were particularly likely to give rise to projection, both small-scale and on a national/international basis.Marie-Louise Von Franz extended her view of projection, stating that "wherever known reality stops, where we touch the unknown, there we project an archetypal image".
Psychological projection is one of the medical explanations of bewitchment used to explain the behavior of the afflicted children at Salem in 1692. The historian John Demos asserts that the symptoms of bewitchment experienced by the afflicted girls were due to the girls undergoing psychological projection of repressed aggression.
Jung wrote, "All projections provoke counter-projection when the object is unconscious of the quality projected upon it by the subject." Thus, what is unconscious in the recipient will be projected back onto the projector, precipitating a form of mutual acting out.
In a rather different usage, Harry Stack Sullivan saw counter-projection in the therapeutic context as a way of warding off the compulsive re-enactment of a psychological trauma, by emphasizing the difference between the current situation and the projected obsession with the perceived perpetrator of the original trauma.
Drawing on Gordon Allport's idea of the expression of self onto activities and objects, projective techniques have been devised to aid personality assessment, including the Rorschach ink-blots and the Thematic Apperception Test (TAT).
Projection may help a fragile ego reduce anxiety, but at the cost of a certain dissociation, as in dissociative identity disorder. In extreme cases, an individual's personality may end up becoming critically depleted. In such cases, therapy may be required which would include the slow rebuilding of the personality through the "taking back" of such projections.
The method of managed projection is a type of projective techniques. The basic principle of the method is that a subject is presented with his own verbal portrait named by the name of another person, as well as with a portrait of his fictional opposition (V. V. Stolin, 1981).
The technique is suitable for application in psychological counseling and might provide valuable information about the form and nature of his or her self-esteem Bodalev, A (2000). "General psychodiagnostics".
Some studies were critical of Freud's theory. Research supports the existence of a false-consensus effect whereby humans have a broad tendency to believe that others are similar to themselves, and thus "project" their personal traits onto others. This applies to good traits as well as bad traits and is not a defense mechanism for denying the existence of the trait within the self.
Instead, Newman, Duff, and Baumeister (1997) proposed a new model of defensive projection. In this view, repressors try to suppress thoughts of their undesirable traits, and these efforts make those trait categories highly accessible--so that they are then used all the more often when forming impressions of others. The projection is then only a by-product of the real defensive mechanism.
And he who [continually] declares [others] unfit is [himself] unfit and never speaks in praise [of people]. And Samuel said: All who defame others, with their own blemish they stigmatize [these others].