Models and modelling are central not only to management but to all human affairs. Models providegrounds for decision making and action-taking. This paper investigates the concept of ‘model’, showingthat the conventional notion of a model as understood in management science, a notion founded onpositivism and realism, is insufficient for the complex practical needs of management models. To remedythis situation, an alternative notion founded on Projective Constructivist Epistemology (PCE) isproposed. Some of the implications of the new notion for modelling practice and model validation are alsodiscussed. The new notion results from theoretical investigations and empirical experience gleaned over thelast five years in public-sector, military and business contexts. The paper concludes with a brief discussionof areas that might merit investigation in the future.