Intolerance of uncertainty (IU) is the tendency to react negatively to uncertain situations. In this review, we critically evaluate the evidence for IU as a cognitive vulnerability for obsessive-compulsive disorder (OCD), including (a) evidence for a robust association between IU and OCD symptoms, (b) evidence that IU is stable and trait-like, (c) evidence for IU as a causal risk factor that influences the development of OCD directly or indirectly, and (d) evidence that IU is malleable to intervention. The available evidence suggests that IU is likely a candidate cognitive vulnerability factor for OCD, though additional research is needed to determine if increasing tolerance for uncertainty is a mechanism of effective OCD treatment. Future research examining IU across multiple levels of analysis and a more rigorous examination of the nomological network of IU may identify specific pathways contributing to the development and maintenance of OCD.