Obsessive-compulsive disorder (OCD) is a prevalent condition, affecting up to 3% of people. Clinical perfectionism is a common feature of OCD, as well as a range of other problems, such as anxiety disorders, depression, and eating disorders, to name a few. This course provides step-by-step, evidence-based approaches for treating OCD, perfectionism, and related problems. Participants will learn about the latest approaches to treatment, including psychological treatments, pharmacological approaches, and newer biomedical treatments, such as deep brain stimulation and d-cycloserine. Most of the course will focus on evidence-based psychological approaches to treating OCD and perfectionism. Attendees will learn about cognitive strategies for challenging the beliefs, interpretations, and predictions that help to fuel OCD and perfectionism. Behavioral approaches (e.g., exposure and response prevention, behavioral activation) will also be discussed. This course will also cover mindfulness and acceptance-based approaches, which have growing support for both OCD and perfectionism. In addition, participants will learn about how to use motivational interviewing to resolve ambivalence, resistance, and disengagement in therapy, how to provide culturally responsive care, and how to deal with complex cases and comorbidity. Finally, the course will discuss the features and treatment of other obsessive-compulsive spectrum disorders, including hoarding disorder, body-focused repetitive behaviors, body dysmorphic disorder, and illness anxiety.