This textbook discusses the principles of queuing theory and teletraffic engineering in telecommunication networks. The book lays out the rigorous theoretical background while keeping strong links to practical applications and real-life scenarios. The overall goal of this textbook is to provide students with in-depth and broad understanding of the operational framework of teletraffic problems, and therefore the capability to select the most suitable and effective method to solve traffic engineering problems that may arise in real-life. The student will learn to pick and choose from a spectrum of tools, ranging from the simplest mathematical treatment to sophisticated models. The book features practical examples derived from real life, presented and discussed, establishing the links with the theoretical results. Pedagogical materials include end-of-chapter exercises and problems.