Intrusive thoughts feature as a key factor in our current understanding of Obsessive–Compulsive Disorder (OCD). Cognitive theories of OCD assume that the interpretation of normal intrusive thoughts leads to the development and maintenance of the disorder. Research that supports the role of beliefs and appraisals in maintaining distress in OCD is based on the supposition that clinical obsessions are comparable to normal intrusive thoughts. This paper reviews research investigating the occurrence of intrusive thoughts in a nonclinical population, in order assess if these thoughts are comparable to obsessions. The prevalence of intrusive thoughts with obsessive content is assessed, as well as other aspects of these thoughts, such as triggers, appraisals and response strategies. Through critique of literature in this field, this paper goes on to discuss the implications for future research.