Major depressive disorder (MDD) is a common, recurrent, and impairing condition that predicts future suicide attempts, interpersonal problems, unemployment, substance abuse, and delinquency (Kessler & Walters, 1998). According to the World Health Organization, 121 million people are currently suffering from MDD and it is a leading cause of disability worldwide among people 5 years old and older. The annual economic cost of MDD in the United States alone is staggering-$70 billion in medical expenditures, lost productivity, and other costs (Greenberg, Stiglin, Finkelstein, & Berndt, 1993;Philip, Gregory, & Ronald, 2003). Further, MDD accounts for more than two-thirds of the 30,000 reported suicides each year (Beautrais et al., 1996). Given this enormous impact at societal and individual levels, there is a clear need to develop and disseminate efficacious treatments for this disorder.Fortunately, a number of empirically supported interventions are available for depressed adolescents and adults. In-depth descriptions of some of the most established treatments are included in this book-Cognitive Behavioral Therapy (CBT), Behavioral Activation (BA), and Cognitive Behavioral Analysis and System of Psychotherapy (CBASP). We include chapters on the application of CBT with adolescents and adults. Further, we include a chapter on how to apply these interventions to diverse populations, such as people with diverse racial and ethnic backgrounds. Each chapter provides a detailed, clinician-focused guide on how to implement these interventions. A review of the research base for each intervention is included in Appendix A.Prior to reviewing the contents of each chapter in this introduction, we first provide an overview of how depression is defined, a brief description of its C01 02/11/2011 8:48:52 Page 2 epidemiology, and then how depression is typically assessed. We then review other treatments (both pharmacological and nonpharmacological) that have empirical support for the treatment of depression but are not included in this volume. We finish with a brief overview of this volume's chapters.