Alongside extensive research into the effectiveness of psychological therapies over the last four decades (see Lambert & Ogles, 2004, for a review), there have been consistent findings that different therapies have equivalent beneficial effects (Luborsky, Singer & Luborsky, 1975; Stiles, Shapiro, & Elliot, 1986; Wampold, 2001). This has evoked interest in factors that are considered to be common to all therapies and an ongoing search for the active ingredients in psychotherapy. This doctoral thesis aimed to offer new insight into these areas by investigating clients' perspectives of the active ingredients in psychological therapy, followed by a review of the therapeutic alliance - a common factor considered to play a critical role in outcome. Section one: the literature review, reports the findings of the meta- synthesis of qualitative studies exploring the client's perspective on the nature of the therapeutic alliance across a range of mental health settings. The review evaluates the current alliance literature, and argues that a re-conceptualization of the therapeutic alliance is warranted. It makes a further case for the role that qualitative analyses may play in expanding our theoretical knowledge in this area, complimenting the work carried out by quantitative endeavours. Section two: the research paper, presents an investigation into clients' perceptions of the mechanisms of change within a psychological therapy programme. Grounded theory methods were used to construct a model from the data, which explained the key mechanisms that facilitated participants' change journey. Following a discussion of the links with existing theory, clinical and methodological implications of the research are offered. Section three: the critical review, offers a reflexive account of the dilemmas, tensions and learning experienced by the researcher throughout the thesis journey.