In this chapter, you’ve been shown the basic principles of how XMPP works, and how XMPP can be used to provide a flexible, extensible, and scalable infrastructure for devices. You’ve learned how brokers help devices cross topology barriers such as firewalls, and how stanzas are related to important communication patterns. You’ve also learned the basics of trust-based communication and loosely coupled interfaces for the IoT. You know how to publish sensor data and control parameters over XMPP and how to test your sensors and actuators using XMPP. In the following chapters, you will learn how to interact with your devices with code.