We provide a review of different approaches to linking model structure to observed behavior with a particular view towards using models for theory building. We identify four such approaches, namely the “classical” approach, the “pathway participation” approach, the “eigenvalue elasticity” approach, and the “eigenvector” approach, respectively. We outline our assessment of the strengths and weaknesses of each approach and point to some main challenges and tasks ahead. We find that the eigenvalue and eigenvector approaches carry the largest potential but that a more solid theoretical foundation of the method is required. Once such a foundation is developed, it will be important to develop intuitive analytical tools that can be of use to a wider system dynamics audience. Since a “grand unified theory” will never be possible, all tools will be based on approximations and it is only in their practical use that we can discover their real value.