Background: Adults with severe/profound intellectual disability typically face poor communication outcomes as they are often nonverbal and need their supporters to provide for their communication needs. This review aimed to identify studies focused on the communication resources people with severe/profound intellectual disability use for functional communication, and the enablers and barriers to functional communication. Methods: Nine databases were systematically reviewed with keywords pertaining to the functional communication of adults with severe/profound intellectual disability. Out of 3427 identified articles, 12 met the inclusion criteria. Hand searches and ancestral searches identified another 4 articles. Out of the 16 articles, two did not meet the quality assessment criteria and were excluded. Thus, 14 articles were included in this review. Results: The findings revealed that picture exchange communication systems is the most common communication system used to support the development of functional communication. The most common functions enabled by the communication systems were choice-making and making requests. Several barriers (e.g., individual factors related to adults with severe/profound intellectual disability, others' attitudes, behaviour and knowledge) to and enablers (e.g., accessibility and availability of the communication system, training for those supporting adults with severe/profound intellectual disability) of functional communication were identified. Conclusions: Removing the barriers and enabling functional communication is essential to developing the functional communication of adults with severe/profound intellectual disability.