With respect to the upcoming DSM-5, various psychological disorders have recently been discussed as possible obsessivecompulsive spectrum disorders based on its similarities and differences to obsessive-compulsive disorder (OCD). Specifically, research groups have discussed the inclusion of a separate OC spectrum category including OCD as well as OC spectrum disorders such as body dysmorphic disorder, dermatillomania, trichotillomania and compulsive hoarding. The aim of this special issue is to provide an overview of the diagnostic criteria and associated features of OCD and OC spectrum disorders as well as to provide some insights on effective treatment strategies.