Extended reality (XR) technologies including virtual and augmented reality are seeing increasing research interest in the field of mental health. Obsessive compulsive disorder (OCD) is a condition that remains difficult to assess and treat despite the availability of effective therapies. This systematic review synthesises the current knowledge regarding the use and effectiveness of XR in the assessment, treatment, and study of OCD. The protocol for this review was registered on PROSPERO (ID: CRD42021248021). Searches of six databases were conducted. The xReality framework was used to define which technologies would be included as XR. Studies that recruited analogue samples as well as clinical OCD populations were included. A narrative synthesis of the findings was planned. There was consistent evidence for the use of virtual reality as a tool for symptom provocation in people with contamination-related OCD, as part of exposure and response prevention. Significant heterogeneity exists between study designs found in both symptom provocation and treatment outcome studies. This review has important implications about the narrow focus of research in this area thus far, highlighting the need for further study of different uses of XR in providing positive treatment outcomes across a broader range of OCD symptoms.