The authors conducted a systematic review of the literature, including studies that used a single-case design (SCD) and taught augmentative and alternative communication (AAC) use to adults with complex communication needs. The purpose of this review was to describe (a) adults receiving AAC intervention, (b) components of the interventions used, and (c) how the literature met quality standards set by the What Works Clearinghouse (WWC). Across the 12 SCD studies included, a total of 28 adults with complex communication needs received intervention. As part of the intervention, the majority of the participants (n = 24; 86%) were introduced to new AAC systems (e.g., picture, communication application). Ten of 12 studies showed at least moderate evidence of effectiveness. Only three of 12 studies met the WWC standards without reservation. Findings from this review call for action to ensure quality AAC access and services are available to adults with complex communication needs.