A cordial welcome to the third edition of Psychotherapy Relationships That Work. This book seeks, like its predecessors, to identify effective elements of the psychotherapy relationship and to determine effective methods of adapting or tailoring that relationship to the individual patient. That is, we summarize the research evidence on what works in general as well as what works in particular. This dual focus has been characterized as “two books in one”: one book on relationship behaviors and one book on adaptation methods under the same cover. In this third edition, we physically separate the “two books” into two volumes as the number of chapters and the amount of research have grown considerably over the past decade. This Volume 1 features evidence-based therapist contributions to the relationship; Volume 2 addresses evidence-based therapist responsiveness to patient transdiagnostic characteristics.