This chapter defines key system theory elements for computational modelling, highlighting the challenges of system dynamics and proposing a framework using dimensions like holisticity, realisticity, and orgitonality. Comparative analysis of modelling paradigms and system simulation programs, alongside the Turing machine concept, underscores their applicability to sustainability focused projects. Two modelling examples, Witness and value stream analysis, illustrate how system translations reveal unique strengths and limitations of each approach. The chapter concludes with broader applications in computational sustainability and future research directions to enhance model integration for addressing complex system challenges.