Theoretic models, such as game-theoretic model, Markov decision processes, linear and non-linear dynamic models, etc., at the system level, play a significant role in Cyber-Physical Systems (CPSs). These models stand as a scientific basis for high-level, security-related decision making. Game theory provides mathematical tools and models for investigating multi-person strategic decision making, where the players or decision-makers compete for limited and shared resources (Manshaei et al., ACM Comput Surv 45(3):25, 2013). Considering the security issues in CPSs, we can view the defenders and attackers as two types of players, who fight for specific resources. Therefore, we use game models to describe the interactions between them. The analytical results based on the game models can assist us in finding the optimal defense strategy. In this chapter, we briefly review specific game theory models, including zero-sum games, Stackelberg games, and FlipIt game. These models are closely related to our applications.