Today, every psychotherapist is willing to stand up for evidence-based psychotherapy. Yet, the field is severely split into factions, each having its own ideas about what needs to be done. Cognitive behavior therapists, psychoanalysts, and postmodernists unite under the common banner of evidence-based psychotherapy against a non-existent opposition, but they war with each other about what counts as sound evidence, what is necessary and what will suffice. Today’s debates mirror and to some degree are identical with earlier ones stretching from the origin of psychotherapy to the present time about the natural science status of the discipline. Should the methodology of natural science be imported into psychotherapy? Can the field be transformed into an applied natural science? Should it? Edward Erwin takes up the basic issues in this book where he discusses causation and content in psychotherapy, the role of scientific realism, debates about the need for randomized clinical trials in assessing effectiveness, the problem of using general methods to deal with unique individuals, and the acceptability in psychotherapy of the objectivist epistemology employed in natural science.