Machine-to-machine (M2M) communication is one of the most challenging parts of implementing IoT systems. The previous chapter briefly discussed how the system communicates with the cloud. This chapter's prime focal point is how two or more devices talk to each other, the methodologies involved, and how one can design such a system. We will also walk you through some of the protocols involved in M2M communication. If you recall the architecture of IoT systems, the part we will focus on is at the edge level. An ideal IoT use case would involve a lot of sensors and controllers all talking to each other via a local network. Here, let's dive deep into these networks and how devices can talk to each other, what protocols are available, what the strategies are, what to use when, and so on. A bunch of concepts will be clarified regarding M2M communication by the end of this chapter.