The deep penetration of computers in all realms of society makes technological change the key driver for changing our lives. This will result in a change in approach, from viewing the role of IT as mainly supporting other disciplines, to the integration of IT concepts, tools and theory into modelling theories of the supported disciplines. This chapter discusses some aspects of the relationship between the IT as a modelling discipline, and the modelling disciplines of the domains where IT is applied. IT deals with data and data processes, while application domain models deal with entities of the domain and how they interact. Cross-competence models must deal with both, and with how models of the information technology discipline relate to the various models of the domain disciplines.