A gentle introduction to the key theoretical ideas underpinning modern elementary particle physics, "Principles of Particle Physics" aims to provide a basic grounding in particle theory whilst avoiding the more advanced topic of quantum field theory. The mathematical language of particle physics is carefully developed and supported by plenty of worked examples showing how relatively simple mathematical ideas can lead to testable predications. The book shows how particle physics is related to other areas of physics and the text draws this out by using examples from many areas, including astrophysics and cosmology. Key ideas are illustrated by reference to simpler applications in atomic physics leading to a greater understanding of basic quantum mechanics. The book includes lots of worked examples and is illustrated throughout with Feynman diagrams and covers the latest developments in theory and experiment, including neutrino oscillations.