For decades the development of evidence-based therapy has been based on experimental tests of protocols designed to impact psychiatric syndromes. As this paradigm weakens, a more process-based therapy approach is rising in its place, focused on how to best target and change core biopsychosocial processes in specific situations for given goals with given clients. This is an inherently more idiographic question than has normally been at issue in evidence-based therapy. In this article we explore methods of assessment and analysis that can integrate idiographic and nomothetic approaches in a process-based era. PBT and the Individual 4 The Role of the Individual in the Coming Era of Process-Based Therapy Questioning assumptions in science is disruptive. Within a defined area of study, a priori analytic assumptions provide the scaffolding for which questions are asked, which methods are used, and which data are deemed relevant. Professionals often view questions, methods, and analytic units simply as the required tools of good science-not reflections of assumptions-and as a result there can be a sense of disorientation when times of upheaval arrive and assumptions are pointed out and critically examined. So it is today within the domain of mental health, and the intervention science linked to it. For decades is has been assumed that a satisfactory field of evidence-based treatment could emerge based on adequate experimental tests of protocols focused on psychiatric syndromes. This protocols for syndromes era had a coherent set of key strategic assumptions built into its scientific and public health strategy-but every one of them is now being openly questioned. At the same time, a powerful alternative strategic agenda is emerging that echoes some of the process-based and idiographic assumptions of the earliest days of behavioral research, as well as the therapy based upon it. We are reminded of that history by the very name of this, the oldest of all of the applied behavioral journals. However, revitalization of the study of change processes that apply idiographically is not a mere repeat of the past, since it encompasses questions, methods, and data that are distinct and new (Hayes & Hofmann, 2017, 2018; Hofmann & Hayes, 2018).