Millions of people attempt to lose weight every year, but most will not succeed. Simply learning about a new diet and exercise plan is not enough. This book presents 25 detailed sessions of an empirically supported, cognitive-behavioral treatment package called acceptance-based behavioral treatment (ABT) that has now been utilized successfully in five large National Institute of Health–sponsored clinical trials. The foundation of this approach is comprised of the nutritional, physical activity, and behavioral components of the most successful, gold-standard behavioral weight loss packages, such as Look Ahead and the Diabetes Prevention Project. These components are synthesized with acceptance, willingness, behavioral commitment, motivation, and relapse prevention strategies drawn from acceptance and commitment therapy, dialectical behavior therapy and relapse prevention therapy. ABT is premised on the idea that specialized self-control skills are necessary for weight control, given our innate desire to consume delicious foods and to conserve energy. These self-control skills revolve around a willingness to choose behaviors that may be perceived as uncomfortable for the sake of a more valuable objective. The treatment focuses on both weight loss and weight loss maintenance and aims to confer lifelong skills that facilitate long-term weight control. This companion Client Workbook contains summaries of session content, worksheets, handouts, and assignments.