This thesis develops an existential-phenomenological understanding of resistance in psychotherapy. It is argued that the concept of resistance is both one of the most problematic, as well as one of the most enduring, concepts within psychotherapy. An in-depth, critical literature review is presented on the various meanings and significances given to resistance across different theoretical perspectives. It is shown that while resistance as a concept belongs centrally within the psychoanalytic perspective, nevertheless, substantial interest and debate about resistance is present within other perspectives. From an existential-phenomenological perspective, the concept of resistance, where this is understood to refer to an unconscious intrapsychic force, is impermissible. However, it is argued that when the concept of resistance is distinguished from the intersubjective phenomenon of resistance, an existential-phenomenological perspective is both possible and desirable. Within the process of psychotherapy, resistance may be understood as a co-constituted 'beingclosed' to the possibilities of relational encounter. Resistance may be understood as one of a range of 'existence tensions'. This view greatly implicates the being of the therapist in this phenomenon. In order to more fully 'ground' such a perspective, a phenomenological investigation of therapists' experiences of 'encountering resistance' in psychotherapy was conducted. The results of this investigation were submitted to a further validation process in a survey study of UK psychotherapists from a range of theoretical perspectives. Additionally, this survey study explored therapists' attitudes and concerns regarding resistance in psychotherapy. The results of both of these studies are further interpreted from an existential-phenomenological perspective. It is argued that a consideration of the meaning and significance of resistance assists in the further development of an existential-phenomenological approach to psychotherapy. Furthermore, it is argued that .an existentialphenomenological perspective on resistance clarifies a phenomenon that is also relevant and important for other models of psychotherapy.