Group memberships provide a system of orientation for self-definition and self-reference in the process of relating to and managing social distance with others, and the use of language and communication serve central roles in the processes. In the nearly four decades since its inception as speech accommodation theory, communication accommodation theory has been used in multidisciplinary, multilingual, and multicultural contexts for understanding when, how, and why we, as speakers, accommodate to each other’s languages and styles of communication. In CAT’s theoretical domain, accommodation refers to the ability, willingness, and strategies to adjust, modify, or regulate individuals’ language use and communication behaviors. Specifically, approximation strategies such as convergence, divergence, maintenance, and complementarity are conceptualized in the earlier developmental stages of CAT, with other strategies such as interpretability, discourse management, and interpersonal control added to the list at later stages. With its strong intergroup features, CAT is a robust theory that offers explicit motivational analysis to account for intergroup communication behaviors and intergroup relations. Blossomed initially in a multilingual and multicultural context in Quebec, Canada in the 1970s, CAT connects well with other existing theories on cultural adaptation, intergroup contact, and intergroup relations. Yet, CAT distinguishes itself from other theories as it attends to the interactive communication acts and processes and relates them to other sociocultural constructs, while interpreting and predicting the social, relational, and identity outcomes.