Cyber-Physical Systems (CPS) represent the convergence of computational algorithms, communication networks, and physical processes. These systems are widely deployed in critical infrastructures such as transportation, healthcare, energy, and industrial automation. While CPS offers enhanced efficiency, automation, and intelligence, it also introduces significant security challenges due to the tight coupling between cyber and physical components. This chapter presents a comprehensive analysis of CPS architecture, major application domains, and associated security threats, including adversarial attacks in AI-enabled CPS. Furthermore, it discusses defense mechanisms, design principles, and emerging research directions to ensure secure and resilient CPS deployments.