The dissertation is a 'critical edition' of a system of actor training based on three main sources: a vocabulary of movement analysis developed by Rudolf Laban in the last years of his life; C. G. Jung's theory of psychological functions and types; and the acting system of C. Stanislavski and his main followers. The three strands were brought together by the dancer and acting teacher Yat Malmgren (1916-2002), who taught his system for over forty years to some of the major figures of world theatre and film: Peter Brook, Pierce Brosnan, Simon Callow, Sean Connery, Anthony Hopkins, Adrian Noble among others. The dissertation is presented in two volumes: - Volume I sets the system in context, historically as well as in terms of current discourses about the nature of acting. It includes a survey of its origins, followed by an in-depth examination of its three main sources, focusing on the central concept of energy in acting. Further chapters describe: a. a systematic, step-by-step psychophysical approach to analysing character, the actor's own self and to ways of bridging the two in the process of transformation. The author captures the salient features of a method of work which informs aspects of Western acting practice. b. the light thrown by the system on the idea of theatre character. The author puts forward the idea of a character 'independent' of both actor and text. c. the applications of the system in training and professional practice, based on interviews with a number of prominent British actors and directors. - Volume II consists of a detailed, annotated description of the system. It is based on a free transcript of recordings of Yat Malmgren's teaching and amounts to a 'manual' for those interested in studying and/or teaching the system. The volume is illustrated throughout. Appendices include original materials derived from Laban's last years of work, published here for the first time.