This cluster of papers covers a wide range of topics related to obsessive-compulsive disorder (OCD) and its related conditions, including Tourette syndrome. The papers discuss the development and validation of assessment tools, various treatment approaches such as cognitive-behavior therapy and deep brain stimulation, neuroimaging studies, genetic associations, and the impact of OCD on neurocognitive functioning. Additionally, there is a focus on specific symptom dimensions, such as hoarding behavior, and the prevalence and epidemiology of these conditions.