This article presents the Renger System Test (RST) as a method for assessing whether a system evaluation approach is suitable for evaluating complex interventions. The RST has three criteria: (1) the intervention includes multiple components, (2) these components operate interdependently, and (3) their interdependence produces an outcome that no single component can achieve alone. An NIH-funded case illustrates how to apply the RST to program source documentation. Findings suggest several key terms can be used to infer whether each of the RST criteria is met. The article discusses the pitfalls of using an intervention's label to select the most appropriate evaluation approach, as well as the challenges when there is a disconnect between the funder-mandated evaluation approach and a better fit-for-purpose system approach.