There has been enormous progress in psychotherapy research. This has culminated in recognition of several treatments that have strong evidence in their behalf. Even so, after decades of psychotherapy research, we cannot provide an evidence-based explanation for how or why even our most well studied interventions produce change, that is, the mechanism(s) through which treatments operate. This chapter presents central requirements for demonstrating mediators and mechanisms of change and reviews current data-analytic and designs approaches and why they fall short of meeting these requirements. The role of the therapeutic alliance in psychotherapy and cognitive changes in cognitive therapy for depression are highlighted to illustrate key issues. Promising lines of work to identify mediators and mechanisms, ways of bringing to bear multiple types of evidence, recommendations to make progress in understanding how therapy works, and conceptual and research challenges in evaluating mediators and mechanisms are also presented.

Psychological interventions to treat mental health issues have developed remarkably in the past few decades. Yet this progress often neglects a central goal—namely, to reduce the burden of mental illness and related conditions. The need for psychological services is enormous, and only a small proportion of individuals in need actually receive treatment. Individual psychotherapy, the dominant model of treatment delivery, is not likely to be able to meet this need. Despite advances, mental health professionals are not likely to reduce the prevalence, incidence, and burden of mental illness without a major shift in intervention research and clinical practice. A portfolio of models of delivery will be needed. We illustrate various models of delivery to convey opportunities provided by technology, special settings and nontraditional service providers, self-help interventions, and the media. Decreasing the burden of mental illness also will depend on integrating prevention and treatment, developing assessment and a national database for monitoring mental illness and its burdens, considering contextual issues that influence delivery of treatment, and addressing potential tensions within the mental health professions. Finally, opportunities for multidisciplinary collaborations are discussed as key considerations for reducing the burden of mental illness.

The long-standing divide between research and practice in clinical psychology has received increased attention in view of the development of evidence-based interventions and practice and public interest, oversight, and management of psychological services. The gap has been reflected in concerns from those in practice about the applicability of findings from psychotherapy research as a guide to clinical work and concerns from those in research about how clinical work is conducted. Research and practice are united in their commitment to providing the best of psychological knowledge and methods to improve the quality of patient care. This article highlights issues in the research- practice debate as a backdrop for rapprochement. Suggestions are made for changes and shifts in emphases in psychotherapy research and clinical practice. The changes are designed to ensure that both research and practice contribute to our knowledge base and provide information that can be used more readily to improve patient care and, in the process, reduce the perceived and real hiatus between research and practice.

The rich research literature on psychotherapies for children, adolescents, and adults has identified several interventions that can ameliorate or effect significant change in psychiatric disorders and a variety of social, behavioral, and emotional problems and can enhance medical outcomes and recovery. After decades of psychotherapy research and thousands of studies, there is no evidence-based explanation of how or why even the most well-studied interventions produce change, that is, the mechanisms through which treatments operate. This article discusses central requirements for demonstrating mediators and mechanisms of change. Also presented are promising lines of work to identify mediators and mechanisms, ways of bringing to bear multiple types of evidence, recommendations to make progress in understanding how therapy works, and conceptual and research challenges in evaluating mediators and mechanisms.