This paper discusses some of the concepts in the theory and practice of transpersonal psychology and the sources from which they have been derived. The basic concept of the 'self as distinct from the ‘ego’ is characteristic of most Eastern philosophies. The use of imagery as a means of contacting unconscious material can be traced back through the esoteric practices of both West and East, its recent applications having been developed by Carl Jung and Roberto Assagioli. Abraham Maslow began modern research into transcendental altered states of consciousness with his research on peak-experiences.