Intellectual disability (ID) and autism spectrum disorders (ASDs) covary at very high rates. Similarly, greater severity of one of these two disorders appears to have effects on the other disorder on a host of factors. A good deal of research has appeared on the topic with respect to nosology, prevalence, adaptive functioning, challenging behaviors, and comorbid psychopathology. The purpose of this paper was to provide a critical review and status report on the research published on these topics. Current status and future directions for better understanding these two covarying disorders was reviewed along with a discussion of relevant strengths and weaknesses of the current body of research.