Applied behavior analysis has become dominated by the study of developmental disabilities and a few other problem areas where direct contingency principles provide relatively adequate guidance for technological development. Basic behavior analysis is struggling for its identity and indeed for its very survival. Both situations are symptoms of the same problem: the failure to provide an adequate account of human language and cognition. In this talk I review the empirical and conceptual progress of Acceptance and Commitment Therapy (ACT). ACT is one of a small number of new third wave interventions that is fundamentally changing modern behavioral and cognitive therapy. In the five years since the first major outcome study on ACT appeared, successful outcome studies have shown that ACT is helpful in the areas of stress, substance abuse, smoking, diabetes, pain, anxiety, psychosis, prejudice, parenting, and other areas. Both the breadth of application of ACT and the data on its processes of change comport with its underlying theory, Relational Frame Theory (RFT). Since the combination of functional contextualism, RFT, and ACT is at its essence an expression and extension of the core assumptions of behavior analysis, empirical and conceptual progress in this area carries with it a broader lesson: It is useful for behavior analysis to embrace the empirical and conceptual analysis of language and cognition, and explore the applied implications of that analysis. There are barriers to be overcome in both the applied and basic areas before the opportunities that lesson affords can be realized, however. If these barriers can be addressed there is little to prevent behavior analysis from becoming much more central to modern psychology without having to abandon any of its core commitments.