Philosophers of science typically focus on the epistemic performance of scientific models when evaluating them. Analysing the effects that models may have on the world has typically been the purview of sociologists of science. We argue that the reactive (or “performative”) effects of models should also figure in model evaluations by philosophers of science. We provide a detailed analysis of how models in financial economics created the impetus for the growing importance of the phenomenon of “passive investing” in financial markets. (...) Considering this case motivates the position that we call contextualism about model evaluation, or _model contextualism_ for short. Model contextualism encompasses standard analyses of the epistemic performance of the model, but also includes their reactive aspects. It entails identifying the _epistemic and contextual import of the model_, the ways in which a model can engender change in the world (which we call the _channels of transmission_), and the _interactions between the epistemic and reactive import of a model_. (shrink)