The foundational theory (including methods) of a discipline provides the essential basis for research and practice within that field. This chapter introduces an array of key foundational theories of SSI. Firstly, as the perception, acquisition and analysis of SSI serve as the first step of SSM, this chapter presents a method for acquiring and analyzing SSI (the “Risk-Management (R-M) method”) and a model for SSI perception and analysis, taking a comprehensive perspective of SSM and SSI and integrating SSI practices in SSM. Secondly, as the integration of SSI is an importance means of realizing the value of SSI and a necessary approach to acquiring and integrating multi-source SSI in the big data environment, the chapter proposes a model of SSI integration in the environment of big data. On this basis, it establishes a theoretical framework of SSI literacy and SSI system according to the abilities required of SSI personnel (SSI literacy) and the primary conditions for SSI operation (SSI system). Finally, building upon these foundations, the chapter introduces a model of intelligent SSI analysis, a theory of evaluating SSI services, a system model of intelligent SSI services, and a causal model of SIF, all aimed at addressing the challenges of SSI operation within SSM.