Just like the rest of the software world, embedded software has defects. Today, embedded software is pervasive-built into automobiles, medical diagnostic devices, telephones, airplanes, spacecraft, and really almost everything. Because defects in embedded software can cause constant customer frustration, complete product failure, and even death, it would seem critical to collect and categorize the types of errors that are typically found in embedded software. Jon Hagar describes the few error studies that have been done in the embedded domain and the work he has done to turn that data into a valuable error taxonomy. After explaining the concept of a taxonomy and how you can use it to guide test planning for embedded software, he discusses ways to design tests to exploit the taxonomy and find important defects in your embedded system. Finally, Jon presents some implications and conclusions he’s drawn from the data and makes recommendations for future error studies the embedded community needs.