Cyber-physical systems (CPS) have broad applications in the automotive, avionics, robotics, healthcare, and power grid, where the cyber components involving information processing and networking closely interact with the physical processes. Conventionally, there is a separate design flow of CPS. For instance, control algorithms managing the physical dynamics are designed using model-based approaches, without considering details of the cyber implementation platforms. Modern CPS are getting increasingly intelligent and connected. A new design methodology taking all the layers of CPS and their interplays into account is being developed, aiming for assurance of safety and security, as well as high robustness and resource efficiency. This chapter presents the technical background of CPS, with an emphasis on the cyber and physical interactions, corresponding to the new design methodology. Case studies on connected autonomous vehicles (CAVs) are used to illustrate the most recent development in CPS.