This chapter will contribute to the discussion in one of the two symposia held at ICTMA-15, in particular the symposium about the role of theory in the research about mathematical modelling. First, the necessity to discuss theoretical approaches in the research about mathematical modelling and the idea of the symposium will be pointed out. Subsequently in the second part of the chapter the role of theory in research will be described more differentially. Finally, the contributions to the symposium are classified concerning the role of theory in the theoretical approach. The chapter closes with open questions still remaining, which may guide future symposia on the topic.