Obsessive-compulsive disorder (OCD) is one of the most destructive psychological disorders. Its symptoms often interfere with work or school, interpersonal relationships, and with activities of daily living (e.g., driving, using the bathroom). Moreover, the psychopathology of OCD is seemingly complex: sufferers battle ubiquitous unwanted thoughts, doubts, and images that, while senseless on the one hand, are perceived as signs of danger on the other hand. The thematic variation and elaborate relations between behavioral and cognitive signs and symptoms can be perplexing to even the most experienced of observers. Cognitive-behavioral models of OCD explain these phenomena and account for their heterogeneity. These models also have implications for how OCD is treated using exposure and response prevention, which research indicates are effective short- and long-term interventions.