Transpersonal Psychology moves beyond traditional psychology. Whilst it includes exploration of our relationship with self, others and the world around us, it also incorporates Internal Transcendent Modalities (ITM's) and External Transcendent Modalities (ETM's).
ITM's are those modalities which occur internally and can be used to move into an expanded state of consciousness such as meditation or dream work.
ETM's are those modalities which lay between science and spirituality and are based on:
Transcendence states of consciousness
Loss of ego
Development of spirituality
Exploring these areas will help clarify what transpersonal psychology is and how it can elevate human potential and transformation.
Transpersonal - beyond or through the personal
Transcendent States of Consciousness
Includes: lucid dreaming, breathwork, meditation, guided visualization, intuition, artwork, near-death experiences, hypnosis, shared-death experiences and psychedelic experiences.
Abraham Maslow provided thirty-five different meanings for transcendence and summarized it as:
Transcendence refers to the very highest and most inclusive or holistic levels of human consciousness, behaving and relating, as ends rather than as means, to oneself, to significant others, to human beings in general, to other species, to nature, and to the cosmos. 
Loss of Ego
Central to the transpersonal perspective is the assumption that transpersonal phenomena involve a fundamental transformation of normal egoic existence to some ultimately more satisfying or valuable condition.
Robin Carhart-Harris tells us that the ego is located in the brain's Default Mode Network (DMN). The ego here is presented in terms of a psychoanalytical theory, as a system which:
Works in concert with and against other processes in the brain to determine the quality of consciousness [...] The relinquishment of “ego” enabled profound existential or “peak” experiences to occur that could have a lasting positive impact on behaviour and outlook.
Development of Spirituality
In the chapter 'The calling to a Spiritual Psychology', of the Wiley Blackwell handbook, the authors state:
Spirituality should be developed as an area of study within, or closely linked with, the transpersonal field, rather than as a wholly separate discipline. For example, a closely related discipline of spiritual psychology might find a place with the larger domain of transpersonal studies, especially insofar as some of the approaches to spirituality involve supernatural notions that place it beyond the reach of conventional science.
Grof & Grof tell us:
Much of the value that transpersonal psychology has contributed to conventional psychological thought has been through use of the term spirituality. For example, one of its key contributions involves reframing some psychological emergencies as being spiritual, rather that psychopathological.
 Hartelius, G., Caplan, M., & Rardin, M. A. (2007). Transpersonal Psychology: Defining the past, divining the future. The Humanistic Psychologist, 35 (2), p. 11.
 Maslow, A. H. (1971). The farther reaches of human nature. New York: Viking. p. 279.
 Michael Daniels, Wiley Blackwell Handbook of Transpersonal Psychology p. 23
 Robin L Carhart-Harris, ‘The Entropic Brain: A Theory of Conscious States Informed by Neuroimaging Research with Psychedelic Drugs’, Frontiers in Human Neuroscience, (2014), 1-17 https://www.frontiersin.org/articles/10.3389/fnhum.2014.00020/full.
 Hartelius, G., Friedman, H.L., Pappas, J.D. (2015) Wiley Blackwell Handbook of Transpersonal Psychology
 Grof, S., & Grof, C. (1989). Spiritual Emergency: When personal transformation becomes a crisis.
The Wiley Blackwell Handbook of Transpersonal Psychology depicts the following areas of study:
Neuroscience and the Transpersonal
Transpersonal Dimensions of Somatic Therapies
Transpersonal approaches to Transformation
Healing and Wellness
Jung, Analytical Psychology and Transpersonal Psychology
Ecopsychology and Transpersonal Psychology
Transpersonal Experience and the Arts
The Emergence of Transpersonal Social Engagement
Revision and Re-enchantment of Psychology
Transpersonal psychology is a section of the British Psychological Society.
From their website:
All the major spiritual and mystical traditions of the world include teachings about the nature of mind and promote practices and lifestyles intended to bring about psychological transformation.
To this end Transpersonal Psychology deals with the spiritual nature of human beings...and investigates spiritual practices and experiences, researching their value and their relationship to the models and concepts of psychology.
Transpersonal psychology combines a variety of approaches in psychology, including behaviorism, cognitive psychology, and humanistic psychology, along with other disciplines, including Eastern and Western philosophy, mysticism, mindfulness and the world’s religions. According to the article “Brief History of Transpersonal Psychology” written by one of transpersonal psychology’s founders, psychiatrist Stanislav Grof, in the International Journal of Transpersonal Studies:
In 1967, a small working group including Abraham Maslow, Anthony Sutich, Stanislav Grof, James Fadiman, Miles Vich, and Sonya Margulies met in Menlo Park, California, with the purpose of creating a new psychology that would honor the entire spectrum of human experience, including various non-ordinary states of consciousness. During these discussions, Maslow and Sutich accepted Grof’s suggestion and named the new discipline “transpersonal psychology.” This term replaced their own original name “transhumanistic,” or “reaching beyond humanistic concerns”.
Dr. Irene Siegel tells us that transpersonal psychology has been an outgrowth of the humanistic psychology
movement whereas in humanistic psychology they believe that spiritual development is part of what makes up the whole person, in a transpersonal psychology philosophy, the spiritual piece of the client is the core piece and everything else revolves around that piece. So transpersonal psychology looks to foster the growth and development of the spiritual part of the person. In conventional psychotherapy we look at psychology in terms of maladaptive to adaptive functioning, normal functioning, and there's a range within that. But in transpersonal psychology they look at the human functioning to go from maladaptive functioning to an expanded type of functioning that includes spirituality, mystical experiences, dream state, multi-dimensional experiences - many parts of the client that's not considered in conventional psychology. So, the goal is not just to heal the client but to help the client really evolve and transcend on a spiritual level... what transpersonal psychotherapy means for me is to set the tone in the therapy
session itself where the client can go beyond just healing trauma to accessing that spiritual core and to developing to their highest potential not just to a norm.
Noel Bell asks "What is Transpersonal Psychotherapy?"
It is alleged that the word “transpersonal” was first introduced into psychology by William James in a 1905 lecture. The word was also used in 1942 by Carl Jung as the German term, überpersonlich, which his English translators rendered as “transpersonal”.
The word trans is derived from the Latin for ‘across’ (to the other side). Only by looking to the spiritual dimension that includes and transcends heredity and environment can we discuss an adequate answer to the problem of human existence. Transpersonal psychotherapy could, therefore, be seen as an approach beyond the personal and seeking the sacred in the daily, ordinary life and consciousness in which people live. It is consciousness that heals, and it is consciousness that frees us from our unconsciousness conditioning.
Transpersonal psychotherapists share a great deal of common ground with therapists from other schools in the way they can reflect back material to the client, mirror to the client, engage in active listening, holding, containing and helping them to seek meaning and so on. But the defining difference in transpersonal psychotherapy, to that of the other approaches, is the active pursuit of the spiritual dimension