Governmental agencies serve individuals with Intellectual Disabilities (ID) and Psychiatric Disabilities (PD) and must consequently communicate with these individuals at multiple points, from interviews with claims representatives to written notices sent to applicants and beneficiaries about highly complex material. We review the social scientific, survey research-based, cognitive testing-based and other relevant literatures regarding effective communication with these individuals. Given the nature of governmental contact with individuals with ID and PD, particular interest falls upon formal written communication, but other modes of communicating factual information (e.g., telephone, in-person) are also within the scope of this literature review. We evaluate what is known regarding the receptive and expressive communicative capacities of these individuals. We attempt to evaluate what is known about the communicative strategies to determine how the literature may inform a set of evidence-based best practices regarding for effective and efficient communication with individuals with ID and PD.