Psychosynthesis is an approach to psychology that was developed by Italian psychiatrist, Roberto Assagioli.

He compared psychosynthesis to the prevailing thinking of the day, contrasting psychosynthesis for example with existential psychology, but unlike the latter considered loneliness not to be "either ultimate or essential".

Assagioli asserted that

"the direct experience of the self, of pure self-awareness... – is true."  

Spiritual goals of "self-realization" and the "interindividual psychosynthesis" – of 'social integration...the harmonious integration of the individual into ever larger groups up to the "one humanity"' – were central to Assagioli's theory.  

Psychosynthesis was not intended to be a school of thought or an exclusive method but many conferences and publications had it as a central theme and centres were formed in Italy and the United States in the 1960s.

Psychosynthesis departed from the empirical foundations of psychology in that it studied a person as a personality and a soul - but Assagioli continued to insist that it was scientific. He developed therapeutic methods beyond those found in psychoanalysis.

Although the unconscious is an important part of his theory, Assagioli was careful to maintain a balance with rational, conscious therapeutical work.

Assagioli was not the first to use the term "psychosynthesis". The earliest was by James Jackson Putnam, who used it as the name of his electroconvulsive therapy. The term was also used by C. G. Jung and A. R. Orage, who were both far closer to Assagioli's thinking than Putnam. C. G. Jung had written, comparing his goals to those of Sigmund Freud,  "If there is a 'psychoanalysis' there must also be a 'psychosynthesis’ which creates future events according to the same laws".   Orage, who was the publisher of the influential The New Age journal, also made use of the term, which he hyphenated as psycho-synthesis. Orage formed an early psychology study group and concluded that what humanity needed was not psychoanalysis, but psycho-synthesis.  

The term was also employed by Bezzoli. Freud, however, was opposed to what he saw as the directive element in Jung's approach to psychosynthesis, and argued for a spontaneous synthesis on the patient's part: "As we analyse...the great unity which we call his ego fits into itself all the instinctual impulses which before had been split off and held apart from it. The psycho-synthesis is thus achieved in analytic treatment without our intervention, automatically and inevitably.’