Augmentative and alternative communication (AAC) as an area of clinical and educational practice involves a myriad of decisions related to the symbols, devices, and strategies from which each client must choose. These decision-making points can be productively informed through evidence from comparative intervention studies. The purpose of this review was to synthesize comparative AAC intervention studies using single-subject experimental designs involving participants with developmental disabilities. Following a systematic search, each qualifying study was reviewed in terms of a priori determined appraisal criteria, and summarized in tabular format. Studies were divided into three groups according to their study of aided approaches, unaided approaches, or a combination of both. Results are discussed in terms of methodological adequacy of the studies and their implications for future research and practice.