A variety of conceptualizations of the relationship between therapist and client, as well as the impact the quality of this relationship has on the client, are reviewed. Different hypotheses about bow the alliance might influence therapeutic progress are also presented. The review pays attention to both the historical and conceptual dimensions of this issue, and provides a summary of the empirical bases of the claims made of the value of a good alliance. The article concludes with a discussion of an integrated model of the alliance and a discussion of the clinical and training implications of our current understanding of this concept.