ugmentative and alternative communication (AAC) is an umbrella term that encompasses the communication methods used to supplement or replace speech or writing for those with impairments in the production or comprehension of spoken or written language. AAC is used by those with a wide range of speech and language impairments, including congenital impairments such as cerebral palsy, intellectual impairment and autism, and acquired conditions such as amyotrophic lateral sclerosis and Parkinson's disease. AAC can be a permanent addition to a person's communication or a temporary aid.

Modern use of AAC began in the 1950s with systems for those who had lost the ability to speak following surgical procedures. During the 1960s and 1970s, spurred by an increasing commitment in the West towards the inclusion of disabled individuals in mainstream society and developing the skills required for independence, the use of manual sign language and then graphic symbol communication grew greatly. It was not until the 1980s that AAC began to emerge as a field in its own right. Rapid progress in technology, including microcomputers and speech synthesis, have paved the way for communication devices with speech output and multiple options for access to communication for those with physical disabilities.

AAC systems are diverse: unaided communication uses no equipment and includes signing and body language, while aided approaches use external tools and range from pictures and communication boards to speech generating devices. The symbols used in AAC include gestures, photographs, pictures, line drawings, letters and words, which can be used alone or in combination. Body parts, pointers, adapted mice, or eye tracking can be used to select target symbols directly, and switch access scanning is often used for indirect selection. Message generation is generally much slower than spoken communication, and as a result rate enhancement techniques may be used to reduce the number of selections required. These techniques include "prediction", in which the user is offered guesses of the word/phrase being composed, and "encoding", in which longer messages are retrieved using a prestored code.

The evaluation of a user's abilities and requirements for AAC will include the individual's motor, visual, cognitive, language and communication strengths and weaknesses. The evaluation requires the input of family members, particularly for early intervention. Respecting ethnicity and family beliefs are key to a family-centered and ethnically competent approach. Studies show that AAC use does not impede the development of speech, and may result in a modest increase in speech production. Users who have grown up with AAC report satisfying relationships and life activities; however, they may have poor literacy and are unlikely to be in employment.

The Convention on the Rights of Persons with Disabilities defines augmentative and alternative communication one of communications as well as display of text, large-print, tactile communication, plain language, accessible multimedia and accessible information and communications technology

American Speech-Language-Hearing Association. (2005). "Roles and Responsibilities of Speech-Language Pathologists With Respect to Augmentative and Alternative Communication: Position Statement". Archived from the original on 13 February 2009. Retrieved 2009-01-23.