Functional contextualism is a modern philosophy of science[1] rooted in philosophical pragmatism and contextualism. It is most actively developed in behavioral science in general and the field of behavior analysis and contextual behavioral science in particular (see the entry for the Association for Contextual Behavioral Science). Functional contextualism serves as the basis of a theory of language known as relational frame theory[2] and its most prominent application, acceptance and commitment therapy.[3] It is an extension and contextualistic interpretation of B.F. Skinner's radical behaviorism first delineated by Steven C. Hayes which emphasizes the importance of predicting and influencing psychological events (including thoughts, feelings, and behaviors) with precision, scope, and depth, by focusing on manipulable variables in their context.