The book is based on the authors’ lecture notes from an upper-division communication networks course taught at the University of California, Berkeley. They have used many textbooks over the years. This book was developed as a material for the course and as a reference book for scholars. The book has 12 chapters. It starts with a chapter called “Internet,” which is an overview of how the Internet works. Then, in chapter 2, parameters such as signal-to-noise ratio are introduced. Chapter 3 explains switched Ethernet, the Aloha network, and hub-based Ethernet. Chapter 4 has information about Wi-Fi, chapter 5 explores routing, and chapter 6 is about Internetworking. Chapter 7 covers the transport layer. Chapter 8 is about mathematical modeling for networks and chapter 9 is about cellular networks. Quality of service (QoS) is presented in chapter 10. Chapter 11 explains how bits are transformed in the physical layer. Chapter 12 covers additional topics such as switches, sensor networks, and the Internet of Things (IoT). Each chapter ends with a summary, problems, and references. I have taught network classes in a higher education institution. Network textbooks either cover the fundamentals and lack material on modern issues or they are voluminous. This unique book fills a gap, covering the fundamentals of current and next-generation networks. It has the right amount of knowledge and content for a one-semester course.