This chapter provides information on single-case research design, the different variations of the design, and the benefits. Single-case designs are simple to implement and best used when studying the effectiveness of a specific intervention or multiple interventions, but not a course of therapy (e.g., eight sessions of cognitive-behavioral therapy). The unique aspect of single-case design is that you can conduct a rigorous study, with a high degree of internal validity, with one or a small number of subjects (Kazdin, 2011) while avoiding the constraints and ethical issues associated with randomly assigning research participants. Singlecase research methods originated in psychology and are ideally suited for fields interested in showing change via intervention. These methods are less likely to be used in the social and biological sciences (Kazdin).