The authors argue that progress in understanding mechanisms of change in psychotherapy has been hindered by inconsistent definitions and measurement of treatment components. They propose a framework that distinguishes between therapy elements that are delivered by therapists, received by clients, and applied by clients in everyday life. This approach aims to improve precision in measuring treatment processes and facilitate research into which intervention components are most effective, for whom, and under what circumstances. Overall, the paper provides a valuable methodological framework for advancing process research and the development of more personalised cognitive-behavioural interventions.