This modern, pedagogic introduction to muon spectroscopy is written with the beginner in the field in mind, but also aims to serve as a reference for more experienced researchers. The key principles are illustrated by numerous practical examples of the application of the technique to different areas of science and there are many worked examples and problems provided to test understanding. The book vividly demonstrates the power of the technique to extract important information in many different scientific contexts, all stemming, ultimately, from the exquisite magnetic sensitivity of the implanted muon spin.