This issue of In Session is devoted to challenges in the treatment of obsessive-compulsive disorder (OCD). The remarkable diversity of symptoms and the comorbidity in OCD pose substantial challenges to practitioners seeking to treat this disorder. After briefly reviewing the clinical features of OCD and its typical treatment, we provide brief descriptions of the six articles this issue comprises. Articles focus on the treatment of OCD with comorbid depression, compulsive hoarding, incompleteness, and repugnant obsessions, and on treatment of children who have OCD. The final article describes pharmacotherapy for OCD. All articles feature case vignettes and provide practitioners with clinical recommendations.