BackgroundA better understanding of what is happening inside the ”black box” of population health interventions is needed because of their inherent complexity. The theory-driven intervention/evaluation paradigm is one approach used for this purpose. However, barriers related to semantic or practical issues stand in the way of its complete integration into evaluation designs.Methods and discussionIn this study, we aimed to clarify how various theories, models, and frameworks could contribute to conceiving a grounded theory, called interventional system theory (ISyT), suitable for understanding the black box of population health interventions and acknowledging their complexity. We suggest that this interventional system theory (ISyT) could guide evaluation processes, whatever evaluation design is applied.ConclusionWe believe that such clarification could contribute to encouraging the use of theories in complex intervention evaluations, and to identifying ways to consider the transferability and the scalability of interventions.