This article defines and reviews the concept of ENGAGEMENT in social interaction. Engagement refers to the level of interpersonal involvement displayed by participants in social situations. Various signals, including both spoken and unspoken signals, display engagement of participants in social exchanges. Engagement has been studied from a variety of perspectives, such as language development in children, educational interactions, human-machine exchanges, and medical encounters. Engagement can be conceptualized from a global level (e.g., engagement of persons with a disability in community life) to a local level (e.g., engagement in a particular conversation). Engagement has not been widely studied in the field of speech-language pathology. Therefore, this special issue on engagement in clinical interactions is offered to provide insights that may help clinicians consider methods of improving clinical practices by heightening client engagement in clinical interactions and communicative exchanges.