Modelers, especially in operational research, are becoming increasingly aware that their role in decision-making raises moral problems. This paper discusses two questions: How do moral issues in modeling arise? How can these moral issues be addressed? I propose a framework that (1) provides tools for discovering moral issues raised by models, and (2) provides practical guidance for solving moral problems in modeling. As regards (1), I discuss three moral perspectives on modeling: a perspective that focuses on the beneficial or harmful consequences of using a model; a perspective that focuses on the intentions of using a model; and a perspective that focuses on whether a model promotes virtuous behavior. In order to achieve practical action guidance, (2), four moral mid-level principles are introduced: (i) The principle of transparency expresses the obligations to explain the structure, assumptions and further properties of the model; (ii) the principle of integrity demands for the application of professional standards; (iii) the principle of comprehensiveness stresses that all moral concerns should be acknowledged thoroughly; and finally, (iv) the principle of efficacy states that models should evaluate moral issues explicitly.