Through the extended evolutionary meta-model, and what ACT found there: ACT as a process-based therapy.

This article is part of a special issue in the devoted to process-based therapy (PBT) or a process-based approach to therapy and the role it plays in harmonizing existing evidence-based treatments. In the present discussion, we focus on acceptance and commitment therapy (ACT) and how it fits into the PBT framework. We describe how viewing ACT through a PBT framework and its organizing rubric-the extended evolutionary meta-model (EEMM)-provides fertile ground to expand the ACT and psychological flexibility models, transforming ACT into a more inclusive and flexible version of itself and giving clinicians wider berth with respect to delivering ACT. The PBT approach allows ACT to incorporate therapeutic elements that are not traditionally part of the framework, including include cognitive reappraisal, interpersonal therapy dynamics, physiological downregulation, and the principle of nonattachment. Importantly, ACT maintains its foundational principles throughout this integration. We provide a case example of how to use PBT methods to conceptualize an ACT case, to illustrate PBT-infused ACT in practice. Finally, we outline possible future directions for ACT as it continues to evolve inside of PBT.