Obsessive-compulsive disorder (OCD) is a heritable condition that is associated with neuropsychological deficits. However, genetic underpinnings are difficult to identify and results have been inconsistent. Reasons for this difficulty may be that multiple genes are involved in the etiology of OCD and that the clinical phenotype of OCD is heterogeneous. The use of cognitive and biological endophenotypes was suggested as a resolution to these problems. Endophenotypes are state independent markers that exhibit a closer relation with genetic underpinnings than the clinical phenotype itself. In the current review, we discuss the current state of research on candidate endophenotypes for OCD and consider implications and future directions. In conclusion, several promising candidate endophenotypes for OCD have been identified, namely response inhibition, performance monitoring, and cognitive flexibility.