This paper proposes a definition of communicative competence for individuals using augmentative and alternative communication (AAC) systems. The proposed definition suggests that communicative competence is a relative and dynamic, interpersonal construct based on functionality of communication, adequacy of communication, and sufficiency of knowledge, judgement, and skill in four interrelated areas: linguistic competence, operational competence, social competence, and strategic competence. Linguistic and operational competencies refer to knowledge and skills in the use of the tools of communication; social and strategic competencies reflect functional knowledge and judgement in interaction. The paper urges future research to validate the proposed definition of communicative competence and suggests some implications for assessment and intervention in the AAC field.