The first wave of behavior therapy countered the excesses and scientific weakness of existing nonempirical clinical traditions through empirically studied first-order change efforts linked to behavioral principles targeting directly relevant clinical targets. The second wave was characterized by similar direct change efforts guided by social learning and cognitive principles that included cognitive in addition to behavioral and emotive targets. Various factors seem to have set the stage for a third wave, including anomalies in the current literature and philosophical changes. Acceptance and Commitment Therapy (ACT) is one of a number of new interventions from both behavioral and cognitive wings that seem to be moving the field in a different direction. ACT is explicitly contextualistic and is based on a basic experimental analysis of human language and cognition, Relational Frame Theory (RFT). RFT explains why …