Preface Network Processor Units (NPUs) are designed for use in high-speed, complex, and flexible networking applications, and they have very unique architectures and soft- ware models. The first generation of NPUs appeared in about 2000, followed by a second generation of specialized NPUs for various segments of networking appli- cations, usually equipped with the traffic managers required by contemporary net- works. NPUs can be compared to Digital Signal Processors (DPSs) that are targeted for high-speed, complex, and flexible signal processing, or to Graphical Processing Units (GPUs) that are required in demanding video processing. Using NPUs is not trivial, and professional engineers have to learn how to use and program these processors. System architects and system engineers must be aware of the capabilities and advantages that NPUs can provide them in designing net- work devices. Since data communications and telecommunications industries are bound to use these devices, I found it necessary to include a basic course on NPUs in my department of Communication Systems Engineering at Ben-Gurion Univer- sity. I have been teaching the subject of NPUs since 2003, and during this period an increasing number of similar courses have been given by other electrical engi- neering, computer science, and communication systems engineering departments worldwide. In addition, many of my graduate students (now engineers) have called specifically to tell me how important this course has been for their professional