On the completion of the first project, you successfully started Python-Arduino interfacing. We also interfaced multiple hardware components, that is, motion sensor and LEDs with Arduino via digital pins. During the project, you learned more about the Firmata protocol while utilizing simple Python methods that helped you to establish a connection between your Arduino board and the Python program. When you are working on complex projects, you need more than basic methods to implement the different features that are required by the projects and their associated electronics components. This chapter is designed to give you a comprehensive experience of interfacing so that you can start working on hard problems from the next chapter onwards. We have described various interfacing protocols at the Python-Arduino and Arduino-to-components levels. This chapter also includes practical examples for these protocols with appropriate code and circuit diagrams...