In this chapter we introduce the reader to the fascinating world of microcontrollers. We assume that the reader has no background in this topic. We begin by describing what a microcontroller is. We then proceed to describe the unique niche microcontrollers occupy as compared to the personal computer (PC). We then describe the systems that are commonly available on a generic microcontroller. We specifically do not discuss a specific brand of microcontrollers but rather describe systems common to most microcontrollers. We then discuss advanced microcontroller features such as digital-to-analog converters (DACs), real-time clock systems, liquid crystal display (LCD) interfaces, and other advanced features. We then discuss how to choose a specific microcontroller for a given application and the steps involved in developing an application. We conclude this chapter with an example based on an automated home control system to unify the system chapter concepts. In the references section we provide supplemental reading material on specific processors [1–11].