In addition to the usual evaluation approach (usually a clinical randomized trial in the sense of the question: does an intervention work), complex interventions require further systematic investigations to prove their effectiveness. The role of the context in which the intervention is delivered is essential here, as is consideration of the question of why an intervention works (or does not work). Detailed recommendations exist for the planning and implementation of effectiveness studies on complex interventions, to which interdisciplinary multimodal pain therapy undoubtedly belongs. In an effectiveness model, concrete, verifiable assumptions are formulated as to how an intervention produces changes that are reflected in the endpoint. This article provides a brief introduction to methodological approaches to effectiveness research on complex interventions and uses the PAIN 2.0 project (01NVF20023) to describe in concrete terms what an effectiveness model for interdisciplinary multimodal pain therapy for the prevention of chronic pain in an outpatient setting might look like.