This book is about the (min,+) algebra and its application to worst-case performances in networks, the network calculus theory. Mastering worst-case delays and memory usage in networks is a quality in soft real-time systems (like the one on the Internet: audio, video, etc.) and a requirement for critical real-time systems (like the cyber-physical ones: aircrafts, factories, etc.). The network calculus theory has been designed, implemented and used to compute such bounds. This book offers an up-to-date overview of this framework, from its mathematical background (the min-plus algebra) to its applications, through its implementations.