Acceptance and commitment therapy: What the history of ACT and the first 1,000 randomized controlled trials reveal

Contextual Behavioral Science (CBS) and Acceptance and Commitment Therapy or Training ("ACT" in either case) are arguably entering their 5th decade of development. This paper describes features of their early history and divides development into three phases, plus a fourth that is just beginning. In the context of that review, it examines what can be learned by a content analysis of the first ∼1000 randomized controlled trials on ACT-based interventions, from 1986 through 2022. The expansive vision of CBS and the early ACT research base defined their breadth as far wider than psychological intervention targeting traditional psychiatric syndromes, emphasizing instead the principles, processes, and components needed for a more generally applicable approach. After an era of scientific establishment, ACT research has expanded globally and topically. Many RCTs now take place in lower- and middle-income countries with cultural and policy environments that give rise to unique research priorities. Finally, based on the ACBS Task Force Report and new research findings, we suggest that ACT research may be entering a new era of personalized and process-based intervention based on new "idionomic" forms of functional analysis.