Relational frame theory (RFT) is a modern behavior-analytic account of language and cognition. This approach focuses on derived relational responding, the behavior of relating events that [Page 2835]have not been previously trained directly, as a core aspect of how verbal processes work. Such a behavioral account provides a framework for understanding how key components of language and cognition develop and function. The implications of RFT have been extended to a variety of areas, most notably in understanding the verbal processes related to psychological problems and their amelioration, particularly through acceptance and commitment therapy (ACT).