Rethinking barriers and facilitators in implementation science: conceptual, methodological, and practical challenges, and ways forward.

Implementation science has long relied on the concepts of barriers and facilitators (B&F) to explain why evidence-based practices succeed or fail. Determinant frameworks such as the Consolidated Framework for Implementation Research and Theoretical Domains Framework have standardized this terminology, offering a common vocabulary to describe influences on implementation processes. However, the increasing maturity of the field exposes conceptual and methodological limitations of the traditional B&F approach. This article critically examines eight interrelated challenges in the identification, measurement, and application of B&F, drawing on theoretical, empirical, and methodological literature.The analysis highlights that B&F are not simple opposites, that they are often based on perceptions rather than mechanisms, and that exhaustive identification may not be feasible or conceptually coherent. Further, measurement and prioritization remain inconsistent, and the dynamic, multi-level, and temporal dimensions of implementation are frequently overlooked. The persistent gap between identifying B&F and linking them to implementation strategies constrains progress toward explanatory and actionable science.Moving beyond descriptive checklists, the paper suggests reconceptualizing B&F as dynamic system properties and adopting methods that capture complexity, mechanisms, and contextual interaction. Strengthening theory-method alignment will enable implementation research to evolve from enumerating determinants toward explaining how change unfolds in real-world systems.