The notion of using program theory (PT) in evaluation has become a mainstream idea in the evaluation discourse, and numerous supposed advantages are associated with it. Conceptually, it has been argued that evaluation approaches ignoring PT treat their evaluands as black boxes, as they pay no attention to the mediating mechanisms between programs and their outcomes. However, the use of PT in evaluation itself resembles a black box, too, as there exists no coherent theoretical framework which explains the mechanisms between the use of PT and better evaluations. This paper presents such a framework. It combines a process model of evaluation, to identify different functions of PT, with existing models of evaluation influence, to show how these functions can contribute to better evaluations. This work is expected to clarify the different functions of PT for evaluation and to make assumptions on the effects of PT empirically testable.#evaluation influence #Program Theory and Theory Driven Evaluation #research-on-evaluation #2011 Conference #theories of evaluation #2011 Conference #evaluation influence #evaluation influence #TheoriesofEvaluation #theories of evaluation #Program Theory and Theory Driven Evaluation #theories of evaluation #ResearchonEvaluation #HowTo #Program Theory and Theory Driven Evaluation