In this thesis I argue the case for a revised epistemology that will enable medical practice to understand more fully the relevance and validity of Spirit Release Therapy (SRT), as a clinical approach to releasing alleged discarnate spirits from the living, in its application for the treatment of a wide range of psychological and physiological disorders. SRT is a modern clinical alternative to religious exorcism for the release of spirit entities from patients that has been emerging in psychiatry and clinical psychology since the early part of the twentieth century, especially in North and South America and in Western Europe. In contrast to positivist scientific assumptions that spirits are created in the minds of the superstitious or the mentally ill, SRT finds earthbound spirits of the deceased that are found to be attached in some way to the living. It treats these spirits with equal compassion to those presenting patients who are unwilling hosts to them. This compassionate approach of SRT contrasts with that of the Roman Catholic tradition which casts out spirits deemed to be ‘evil’ using its Rite of Exorcism. The general reaction from modern medicine to the proposition that spirits exist, is to reject it because there is no scientific framework that can accommodate it. Although there is no consensus within the Christian tradition that affirms the existence of autonomous spirits (with many believing in the reality of spirits and evil as symbolic and not metaphysical truths), the Catholic tradition relies on faith and non-rational beliefs in its justification for the eradication of what it consequently regards as inherently diabolical entities. There is therefore a dichotomy between modern medicine and religious belief, but I shall argue that the gulf between these opposing positions can be bridged through an epistemological approach that is both grounded in subjective experience and validated by scientific enquiry. In this thesis I examine the relevance of this epistemological approach to the reality of spirit possession (and the practical procedures adopted in SRT for the possible dispossession of spirits) through an analysis of the conceptual framework and scientific methods of Frederic Myers (1843-1901), the 19th century researcher and co-founder of the Society for Psychical Research. In Part I of this thesis I place spirit possession in a Western social and cultural context where I discuss the contemporary attitudes to spirit possession, which are themselves expressed and reinforced by an epistemology that is grounded in the empiricism of the iii social sciences, anthropology, psychiatry and the scientific study of beliefs. Part II explains Myers’ 19th century methods and theories that challenge positivistic empiricism and Part III seeks to update these methods and theories within a 21st century context where they are applied to various enigmatic case studies that challenge modern psychiatry and clinical psychology. I have adopted this structure in order first to highlight some of the deficiencies of current scientific methods in making sense of spirit possession and second to raise important questions that remain unanswered by mainstream psychology, thereby further illuminating the limitations of the epistemological grounding of this discipline.