This article introduces a new approach to program theory evaluation called theory-based stakeholder evaluation or the TSE model for short. Most theory-based approaches are program theory driven and some are stakeholder oriented as well. Practically, all of the latter fuse the program perceptions of the various stakeholder groups into one unitary program theory. The TSE model keeps the program theories of the diverse stakeholder groups apart from each other and from the program theory embedded in the institutionalized intervention itself. This represents, the authors argue, an important clarification and extension of the standard theory-based evaluation. The TSE model is elaborated to enhance theory-based evaluation of interventions characterized by conflicts and competing program theories. The authors argue that especially in evaluations of complex and complicated multilevel and multisite interventions, the presence of competing theories is likely and the TSE model may prove useful.