This comprehensive volume represents the first state-of-the-art handbook to appear in the field of process research in over a decade. Updating and expanding upon Kiesler's groundbreaking work (1973), Greenberg and Pinsof present here the most systems for understanding the mechanisms of change in individual, group, and family treatment. Special attention is given to the role of the alliance between therapist and client. Emphasizing the impact that empirical investigations can make on practice, the Handbook presents a wide variety of up-to-date process research systems and consolidates methodological information in the field.