Augmentative and alternative communication (AAC) is an area of clinical practice that involves the supplementation or replacement of natural speech for individuals whose natural speech is inadequate to meet their daily communication needs. AAC focuses on patient-specific communication (re)habilitation options for individuals with varied diseases, disorders, and disabilities. A wide range of AAC options are available, from low-tech systems, such as photographs or simple paper-based communication boards or books, to high-tech systems, such as sophisticated voice output computers. This entry provides an overview of the relevant clinical populations, the nature of AAC, and the clinical process in AAC.