This chapter highlights the impact of the recent changes in diagnostic classification that have taken place in the Diagnostic and Statistical Manual (DSM). It discusses the diagnostic features of Obsessive–Compulsive Disorder (OCD). OCD is an intriguing and often debilitating syndrome characterized by the presence of two distinct phenomena: obsessions and compulsions. Hoarding is a distinct disorder in DSM‐5. Hoarding Disorder (HD) can be comorbid with OCD. The Hoarding Rating Scale‐Interview (HRS‐I) is a 5‐item, semi‐structured interview with good internal consistency and reliability, which includes difficulty discarding, difficulty using rooms due to clutter, excessive acquisition, emotional distress, and functional impairment. Deep brain stimulation (DBS), which involves stimulation with an electrical current at sites deep in the brain rather than on the surface, is a more recent technique that is currently under investigation.